CHAPTER 2

PROJECT ALTERNATIVES

This chapter describes the alternatives that were analyzed in the Draft Environmental Impact Statement (DEIS), project alternatives that were initially considered but withdrawn from consideration prior to preparation of the DEIS, the reasons for their withdrawal, and identification of the Preferred Alternative.

The Metropolitan Transportation Commission (MTC) is the transportation planning, coordinating, and financing agency for the nine-county San Francisco Bay Area. It functions both as the region’s transportation planning agency (RTPA) and as the region’s metropolitan planning organization (MPO)—state and federal designations, respectively. The Regional Transportation Plan (RTP), which MTC prepares, is a comprehensive guide for the development of mass transit, highway, airport, seaport, railroad, bicycle, and pedestrian facilities within the Bay Area. The MTC also allocates state and federal funds for transportation projects based on compatibility with this plan.

The MTC-recommended alternative included in this FEIS is Replacement Alternative N-6, self-anchored suspension design variation with a bicycle/pedestrian path. The California Department of Transportation (Caltrans) and Federal Highway Administration (FHWA) identified Replacement Alternative N-6 as the Preferred Alternative. The Preferred Alternative has been identified as the Least Environmentally Damaging Practicable Alternative (LEDPA) in consultation with the U.S. Environmental Protection Agency (EPA) and the U.S. Army Corps of Engineers (ACOE). See Section 2.2.6 ­ Preferred and Least Environmentally Damaging Practicable Alternative for more details.

Pursuant to the National Environmental Policy Act (NEPA), the EIS identifies environmental impacts and values of all reasonable alternatives in sufficient detail to enable decision-makers to evaluate their comparative merits. The East Span Project is a seismic safety project and does not change bridge capacity. As such, a Major Investment Study (MIS) for the SFOBB corridor was not prepared. Identification of the Preferred Alternative occurred following circulation of the DEIS for a 60-day public review period and consideration of all public comments received. Responses to all substantive comments have been prepared and can be found in Volume II, Section I ­ DEIS Comments and Responses.

The No-Build Alternative does not satisfy the project purpose and need. It is presented and evaluated as a basis of comparison with the reasonable alternatives. As noted in Chapter 1, Caltrans added selected minimal seismic strengthening and stiffening elements to the existing East Span structure as an interim measure. That project, completed in summer 2000, received environmental approval pursuant to NEPA and is not evaluated as an alternative in this Final EIS. The No-Build Alternative assumes completion of this interim work.

2.1 INTRODUCTION

2.1.1 Development of Alternatives

Caltrans has performed preliminary engineering and impact analysis on a range of possible project alternatives in the EIS. The retrofit and replacement alternatives, along with the No-Build Alternative, are described in Section 2.2. Replacement bridge design variations considered in the DEIS are described in Section 2.3, including design variations incorporated into the Preferred Alternative. Section 2.4 provides a comparison of the alternatives, including costs, constructibility, and potential to meet the purpose and need. Section 2.5 discusses multi-modal options for alternatives, and Section 2.6 describes construction scenarios for each of the build alternatives. Section 2.7 describes the alternatives, design variations, and detour options that were considered and subsequently withdrawn from further consideration and the reasons for their withdrawal.

The range of alternatives considered in the EIS was established by Caltrans and FHWA in accordance with NEPA requirements and in consultation with permitting and regulatory agencies under guidance of the NEPA/404 Integration Memorandum of Understanding (NEPA/404 MOU). The NEPA/404 integration process is implemented when a project has the potential to affect waters of the U.S. under the jurisdictional authority of the U.S. Army Corps of Engineers (ACOE), and it is anticipated that an individual Section 404 permit will be required. Participants considered options and provided written concurrence on the range of alternatives and the criteria established for selection of alternatives. The following criteria were agreed upon by the NEPA/404 signatories:

Consistent with the NEPA/404 MOU, NEPA/404 integration process signatories (ACOE and EPA) also concurred on the identification of the Least Environmentally Damaging Practicable Alternative (LEDPA). (See Appendix F for the concurrence letters from the NEPA/404 signatories.)

2.1.2 Project Limits/Location

The SFOBB crosses San Francisco Bay in an east-west direction in the central portion of the San Francisco Bay Area and provides a travel route between San Francisco and Alameda counties (see Figure 2-1 in Appendix A). The bridge touches down near Pier 26 in San Francisco and in northwest Oakland between the East Bay Municipal Utility District (EBMUD) wastewater treatment facility and the Emeryville Crescent. The West and East Spans of the bridge are connected on YBI by viaduct sections on either side of the YBI tunnel. A main navigation opening channel is located between Columns E2 and E3 of the SFOBB East Span. The channel, shown on Figure 2-2 (Appendix A), is 405 meters (1,328 feet) wide, with vertical clearance of 60 meters (197 feet) above Mean Sea Level (MSL).

The East Span Project will retrofit and/or replace the portion of the SFOBB between the eastern portal of the YBI tunnel and the SFOBB Toll Plaza in Oakland. The western project limit is the eastern portal of the YBI tunnel; however, project-related traffic controls may extend to the western portal of the YBI tunnel and project signage may extend to the west approach in San Francisco. The eastern project limit is located approximately 400 meters (1,312 feet) west of the toll plaza on a spit of land referred to as the Oakland Touchdown area. The project area limits are shown on Figure 2-2 (Appendix A). The project area is defined as the area within the project limits in which temporary and permanent structures would be placed by any of the alternatives and defines the area within which construction activities, including temporary detours, would be expected to occur. The project area widens over water to allow for marine construction activities. In addition, Bay waters on the north side of YBI are included within the project area to allow staging for the delivery of bulk materials and construction equipment by barge or vessel to staging areas on YBI.

2.2 ALTERNATIVES CONSIDERED

Five alternatives, No-Build, Retrofit Existing Structure, Replacement Alternatives N-2, N-6, and S-4, were considered for the East Span Project. Replacement Alternatives N-2 and N-6 are aligned to the north of the existing bridge and Replacement Alternative S-4 aligns south of the existing bridge (see Figure 2-3 in Appendix A). Alignment drawings for the build alternatives are presented in Appendix A (see Figure Series 2-4, 2-7, 2-10, and 2-11). In order to reroute traffic around the construction area while portions of the existing East Span are dismantled and a new transition structure is completed where the existing bridge now stands on YBI, temporary detours would be required on YBI for the three replacement alternatives (N-2, N-6, and S-4).

Caltrans completed a separate Pile Installation Demonstration Project (PIDP) in December 2000 to provide empirical data to contractors and resource agencies about pile driving in the Central Bay. Three test piles were installed as part of the PIDP. The three installed piles would not be used as structural components of any build alternative, though they would be left in place during construction of the East Span Project and could be used for barge mooring. Prior to completion of the East Span Project, all build alternatives would include removal of these three test piles to an elevation of at least 0.46 meter (1.5 feet) below the mudline, to be measured at the time of removal.

In order to connect the new bridge with the existing retrofitted viaduct on YBI and the SFOBB Toll Plaza at the Oakland Touchdown area, all three replacement alternatives would require dismantling the existing East Span structure. Dismantling would also be required by USCG regulations. A description of the dismantling process is provided in Section 2.6.3.

2.2.1 No-Build Alternative

The No-Build Alternative would retain the existing SFOBB East Span and only assumes the seismic improvements that were completed under the Interim Retrofit Project. The Interim Retrofit Project strengthened bents and columns on the viaduct section on YBI and strengthened or stiffened columns, bents, and trusses at selected locations on the structure, so that the existing East Span would be able to withstand a smaller and more probable earthquake. This work was completed during summer 2000. The No-Build Alternative is evaluated primarily as a basis for comparison with the build alternatives.

2.2.2 Replacement Alternative N-6 (Preferred Alternative)

Replacement Alternative N-6 would construct a 3,514-meter long (11,526-foot long) new bridge north of the existing East Span and dismantle the existing structure. (See Figures 2-10.1a through 2-10.5b in Appendix A).

The western limit of construction for Replacement Alternative N-6 is the eastern portal of the YBI tunnel; however, the limits of work may extend to the western approach of the West Span in San Francisco due to project-related traffic controls and signage. Part of the existing YBI East Viaduct would be retrofitted, modified, partially demolished, and reconstructed. At Bent 48 (see Figures 2-10.1a through 2-10.1c in Appendix A), the new bridge begins with transition structures separating the double-decked lanes into two parallel structures. Outrigger supports would be used to support the upper deck as the lower deck transitions to a structure parallel with the upper deck. The parallel structures curve, enter a tangent or straight section over the existing main navigation opening, curve, then align on tangent toward the Oakland Touchdown area. The parallel structures reach the Oakland shore along the northern edge of the existing Oakland Touchdown area and conform to the existing traffic lanes west of the SFOBB Toll Plaza.

Replacement Alternative N-6 consists of two parallel structures supported by 25 piers over water and 19 bents, set on YBI, and the Oakland Touchdown area. The structures would each be 25.07 meters (82 feet) wide and typically separated by 15 meters (50 feet). The typical roadway section for each bridge deck consists of five lanes, each 3.6 meters (12 feet) wide, left and right shoulders, each 3 meters (10 feet) wide, and traffic barriers (see Figure 2-8 in Appendix A). A 4.7-meter (15.5-foot) bicycle/pedestrian path would be located on the south side of the eastbound deck, 0.3 meter (1 foot) above the roadway elevation and includes viewing areas or belvederes. The five belvederes on the skyway would be 12 meters (39 feet) long by 1.2 meters (4 feet) deep. Caltrans is still investigating whether to include one or two belvederes on the main span that would be 20 meters (66 feet) long by 1.2 meters (4 feet) deep. A simulation of a belvedere design is shown on Figure 2-24 in Appendix A.

The height of the bridge, including the transition structure and the parallel structures, would vary in elevation from 50-55 meters (164-180 feet) above Mean Sea Level (MSL) at the YBI East Viaduct to 5 meters (16 feet) above MSL at the Oakland Touchdown. A typical profile for replacement alternatives is presented in Figure 2-9 in Appendix A.

2.2.3 Replacement Alternative N-2

Replacement Alternative N-2 would construct a new 3,479-meter long (11,411-foot long) new bridge north of the existing East Span and dismantle the existing structure. (See Figures 2-7.1a through 2-7.5 in Appendix A). The alignment parallels the existing bridge and maintains minimal clearance between the old and new structures to accommodate construction of the new bridge and dismantling of the existing structure.

The western limit of construction for Replacement Alternative N-2 is the eastern portal of the YBI tunnel; however, the limits of work may extend to the western approach of the West Span in San Francisco due to project-related traffic controls and signage. The existing YBI East Viaduct would be retrofitted, modified, partially demolished, and reconstructed. At Bent 48 (sees Figure 2-7.1a and 2-7.1b in Appendix A), the new bridge would begin with new transition structures separating the double-decked lanes to two parallel structures. Outrigger supports would be used to support the upper deck as the new lower deck transitions to a structure parallel with the new upper deck. The parallel structures would curve, enter a tangent (or straight section) over the existing main navigation opening, curve, and align on tangent toward the Oakland Touchdown area. The parallel structures would reach the Oakland shore along the northern edge of the existing Oakland Touchdown area and conform to the existing traffic lanes to the west of the SFOBB Toll Plaza.

Replacement Alternative N-2 would consist of two parallel structures supported by 22 piers over water and 19 bents set on YBI and the Oakland Touchdown area. The structures would each be 25 meters (82 feet) wide and separated by 15 meters (50 feet). The typical roadway section for each bridge deck would consist of five lanes, each 3.6 meters (12 feet) wide, left and right shoulders, each 3 meters (10 feet) wide, and traffic barriers. A 4.7-meter (15.5-foot) bicycle/pedestrian path would be located on the south side of the eastbound deck, 0.3 meter (1 foot) above the roadway elevation and includes viewing areas or belvederes. The five belvederes on the skyway would be 12 meters (39 feet) long by 1.2 meters (4 feet) deep. Caltrans is still investigating whether to include one or two belvederes on the main span that would be 20 meters (66 feet) long by 1.2 meters (4 feet) deep. A simulation of a belvedere design is shown on Figure 2-24 in Appendix A.

The height of the bridge, including the transition structure and the parallel structures, would vary in elevation from 50 to 55 meters (164 to 180 feet) above MSL at the East Viaduct on YBI to 5 meters (16 feet) above MSL at the Oakland Touchdown. A typical profile for replacement alternatives is presented in Figure 2-9 in Appendix A.

2.2.4 Replacement Alternative S-4

Replacement Alternative S-4 would construct a 3,550-meter (11,644-foot) long bridge south of the existing East Span and dismantle the existing structure. (See Figures 2-11.1a through 2-11.5 in Appendix A.) Replacement Alternative S-4 was developed to minimize bridge length, avoid use of flat land to the north of the existing East Span on YBI and avoid an in-Bay crossing with the EBMUD sewer outfall located to the south of the existing East Span (see Figure 2-3 in Appendix A).

The western limit of construction for Replacement Alternative S-4 is the eastern portal of the YBI tunnel; however, the limits of work may extend to the western approach of the West Span in San Francisco due to project-related traffic controls and signage. The existing YBI East Viaduct would be retrofitted, modified, partially demolished, and reconstructed. At Bent 48 (see Figures 2-11.1a and 2-11.1b in Appendix A), the new structure would begin with new transition structures separating the double-decked lanes to two parallel structures. Outrigger supports would be used to support the upper deck as the lower deck transitions to a structure parallel with the upper deck. The parallel structures would curve, enter a tangent or straight section over the existing main navigation opening, curve gradually, and align toward the Oakland Touchdown area. The parallel structures would reach the Oakland shore to the south of the existing East Span and transition to the existing roadway west of the SFOBB Toll Plaza.

Replacement Alternative S-4 would consist of two parallel structures supported by 23 piers over water and 19 bents set on YBI, and the Oakland Touchdown area. The structures would each be 25.07 meters (82 feet) wide and separated by 15 meters (50 feet). The typical section for each bridge deck would consist of five lanes, each 3.6 meters (12 feet) wide, left and right shoulders, each 3 meters (10 feet) wide and traffic barriers. A 4.7-meter (15.5-foot) bicycle/pedestrian path would be located on the south side of the eastbound deck, 0.3 meter (1 foot) above the roadway elevation and includes viewing areas or belvederes. The five belvederes on the skyway would be 12 meters (39 feet) long by 1.2 meters (4 feet) deep. Caltrans is still investigating whether to include one or two belvederes on the main span that would be 20 meters (66 feet) long by 1.2 meters (4 feet) deep. A simulation of a belvedere design is shown on Figure 2-24 in Appendix A.

The height of the bridge, including the transition structure and the parallel structures, would vary in elevation from 50-55 meters (164-180 feet) above MSL at the East Viaduct to 5 meters (16 feet) above MSL at the Oakland Touchdown. A typical profile for the replacement alternatives is presented in Figure 2-9 in Appendix A.

2.2.5 Retrofit Existing Structure Alternative

Interim seismic retrofit work on the existing East Span was completed at the Oakland Touchdown area in 1998 and in the summer of 2000 on the truss spans and cantilever main span sections, but these are not components of the Retrofit Existing Structure Alternative. This alternative would retrofit the existing SFOBB East Span to withstand a maximum credible earthquake (MCE) on the San Andreas or Hayward faults. The seismic retrofit strategy of this alternative is based on isolating the superstructure from the substructure (towers and foundations). This work would include constructing additional large diameter piles and new pile caps around the existing foundations, strengthening and stiffening the towers, installing isolation bearings at the top of the towers, and strengthening and/or stiffening the superstructure truss members. Two new large deepwater columns would be added to the cantilever span in the main navigation opening.

However, constrained by a 1930s level of material and construction technology and the complexity of the structure, it is impossible to retrofit the existing East Span to lifeline standards with any reasonable degree of confidence. The seismic capacity of many of the existing materials, the interaction of major structural elements during a seismic event, and the condition of existing foundations are all uncertain. Although substantial modifications to the East Span are proposed as a part of the Retrofit Existing Structure Alternative, it is nevertheless anticipated that substantial damage would occur as a result of an MCE and require extensive reconstruction or replacement. Potential modes of failure are the superstructure unseating from the towers, a failure of column support due to a lack of sufficient reinforcement, the concrete foundations snapping from the tops of the timber piles, structure members bending in the cantilever section, and mangled deck joints that could impede traffic. Replacement would be necessary if structural safety criteria could not be met through repairs to the damaged bridge.

If damage is such that repair of the cantilever section is feasible, this may require complete closure of the East Span from six months to one year. If, however, damage is sufficiently severe that replacement becomes necessary, the East Span would be completely closed for a substantially longer period of time.

The Retrofit Existing Structure Alternative would retrofit both the existing East Span and the East Viaduct section on YBI. The alignment of the bridge would remain unchanged and the bridge would remain a double-deck structure. (See Figures 2-4.1 through 2-4.4 in Appendix A.) Each deck roadway cross section would also remain the same, five 3.5-meter (11.5-foot) wide lanes with no roadway shoulders.

Portion of East Span in Bay

The seismic retrofit strategy for the Retrofit Existing Structure Alternative is based on strengthening and stiffening the substructure (below deck towers and foundations) and isolating the superstructure. Large-diameter piles would be added around the perimeter or on both sides of all existing foundations. New, larger pile caps would be constructed to join the expanded foundations with the existing foundations. Figures 2-5 and 2-6 (Appendix A) show the "before" condition and the "after" simulation of the retrofitted bridge.

The tower legs in the main navigation opening would be encased in concrete. Isolation bearings would be installed on the tops of towers to isolate the superstructure from the substructure and allow differential horizontal movements of approximately 1.2 meters (4 feet) between the two to minimize force transfer during earthquake events.

Two new columns (E2A and E2B) would be added to the cantilever main span just east of YBI (see Figures 2-4.1 and 2-4.2 in Appendix A for locations of new columns).

The seismic retrofit strategy would also add a new edge truss to restrict deformations in the cantilever section. An edge truss is a spanning horizontal truss beam that is extended from the bottom of the lower deck to the bottom of the upper deck (see Figure 2-6 in Appendix A). Retrofitting truss members would include wind bracing and strengthening floor grid and vertical members.

Portion of East Span on Yerba Buena Island

The Retrofit Existing Structure Alternative would strengthen the East Viaduct and columns. The substructure of the East Viaduct would be retrofitted by enlarging and encasing selected columns and footings in concrete, adding cast-in-drilled-hole piles/tie-downs under the footings, enlarging the footings and the pile caps, and installing isolation bearings at the top of columns, and strengthening the deck by replacing expansion joints. Columns YB2, YB3, and YB4 would be encased in concrete and the foundations would be expanded.

2.2.6 Preferred and Least Environmentally Damaging Practicable Alternative (LEDPA)

In December 1998, after a thorough evaluation of project alternatives and consideration of comments from the public and agencies on the DEIS, Caltrans identified Replacement Alternative N-6, self-anchored suspension design variation, including a bicycle/pedestrian path, as its Preferred Alternative. In October 2000, FHWA also identified Replacement Alternative N-6 as the Preferred Alternative.

The Preferred Alternative has been identified as the Least Environmentally Damaging Practicable Alternative (LEDPA) by ACOE (on February 12, 2001) and EPA (on March 15, 2001). Documentation letters can be found in Appendix F. Identification of Replacement Alternative N-6 as the Preferred Alternative and the LEDPA in this FEIS has been coordinated through the NEPA/404 Integration MOU. The LEDPA is identified under the Federal Clean Water Act Section 404 (b)(1) alternatives evaluation process. The Section 404 (b)(1) process requires the ACOE, with input from the EPA, to make a determination of the LEDPA for any action involving discharge of dredge or fill material into waters of the U.S.

As a result of the alternatives analysis process undertaken for the East Span Project, it was determined that Replacement Alternative S-4 would have fewer permanent impacts to special aquatic sites protected by Section 404. Based on the 1999 eelgrass survey, Replacement Alternatives N-2 and N-6 would permanently affect 1.36 hectares (3.36 acres) of sand flats and 0.22 hectare (0.55 acre) of eelgrass, whereas Replacement Alternative S-4 would permanently affect 0.01 hectare (0.02 acre) of sand flats, 0.05 hectare (0.12 acre) of wetland and 0.15 hectare (0.37 acre) of eelgrass.

The "Guidelines for Specification of Disposal Sites for Dredged or Fill Material" (40 CFR 230) state that a Section 404 permit shall not be issued for discharge of dredged or fill materials into waters of the U.S. if there is a practicable alternative which would have less adverse impacts on the aquatic ecosystem, so long as the alternative does not have other significant adverse environmental consequences (40 CFR 230.10(a). An alternative is practicable if it is available and capable of being done after taking into consideration cost, existing technology, and logistics in light of overall purpose (40 CFR 230.10(a)(2)). Although Replacement Alternative S-4 would have fewer impacts on eelgrass and sand flats, it would pose several logistical problems that render it not practicable. Replacement Alternative S-4 would take land from an operating USCG facility, thereby constraining the mission of that facility; it uses land from a Section 4(f) resource (Gateway Park) for which there are prudent and feasible alternatives that avoid that use; it compromises the operation of an important sewer outfall that serves over 610,000 people along the east side of the Bay; it results in more complex construction to protect that outfall; and it results in more extensive and more difficult in-Bay construction because of considerably greater depth to bedrock to construct the main span tower. As a result of these logistical impediments, Replacement Alternative S-4 does not meet the standards for practicability as defined in the Section 404 guidelines.

Replacement Alternatives N-2 and N-6 meet the Section 404 standards of practicability. The following are the key logistical benefits of these alternatives:

Replacement Alternatives N-2 and N-6 are the practicable alternatives pursuant to Section 404 of the Clean Water Act, and they are also feasible and prudent alternatives with the least net harm to Section 4(f) resources. Replacement Alternative N-6 has been chosen as the Preferred Alternative over Replacement Alternative N-2 on the basis of greater ease of construction of the main tower based on geologic conditions, aesthetic benefits such as enhanced drivers’ views, and consistency with the regionally preferred alignment and design features as expressed by the MTC.

2.3 REPLACEMENT ALTERNATIVES DESIGN VARIATIONS

Replacement alternatives are proposed as two parallel skyway structures, each having five traffic lanes, inside and outside shoulders, and a bicycle/pedestrian path on the south side of the eastbound deck. Design variations identified for the replacement alternatives are limited to the type of bridge to be constructed over the main navigation opening. For the portion of the span between the east side of the navigational channel and the Oakland Touchdown, a skyway design (a span supported from under the bridge deck) is the most practical structure type because of the alignment, the geology, the seismic characteristics, shallow water, and deep Young Bay Muds in that area. Other structure types could be built in this area; however, because of the site conditions, they would substantially increase design and construction costs and the time needed to construct. Designing these other structure types to a lifeline standard would also be much more difficult.

It has been determined that for the main span, steel would be used to construct the main tower and superstructure and a steel/concrete composite would be used to construct the substructure. For the skyway, concrete would be used for the superstructure and concrete or a steel/concrete composite would be used for the substructure. For the Oakland Touchdown portion of the bridge, concrete would be used to construct the superstructure and the substructure.

Selection of the superstructure type to be used for the bridge was based on seismic engineering and cost analyses, material availability, maintenance requirements, and impacts to construction schedule. To minimize costs, the span lengths were maximized, which increased load demands. While a 5-meter (16.4-foot) deep structure depth is sufficient for most of the span, it is insufficient to resist the bending and shear demands at the piers, so the superstructure had to be deepened at those points. As a result, a "haunched", or slightly arched, design was selected for the superstructure. This type of superstructure is thick at either end where it sits on a column. (See Figure 2-23 in Appendix A).

2.3.1 Main Span Types

For the replacement alternatives, design variations were considered for the main span section that crosses the main navigation opening. A number of bridge types, as discussed below, were evaluated by MTC’s Bay Bridge Design Task Force Engineering and Design Advisory Panel (EDAP) based on seismic performance, aesthetic considerations, costs, ability to construct the bridge as soon as possible due to seismic vulnerability, and the possible location of a bicycle/pedestrian path. The public had an opportunity to participate during this process at 34 Task Force and EDAP meetings and through letters, phone calls, and e-mails received by MTC. In June 1998, based on the recommendations of the EDAP, MTC voted for a self-anchored suspension design that includes a single tower of 160 meters (525 feet) in height above MSL and maintains the main navigation opening east of YBI.

EDAP’s recommendation was based on seismic safety and the aesthetic value of the bridge. The seismic safety of the self-anchored suspension design was judged to be equal to that of the single-tower, cable-stayed span; however, its aesthetic value was judged to be greater and more visually consistent with the tradition of suspension bridges in the central Bay. In addition, this design involves fewer long-term maintenance costs than the cable-stayed design variation evaluated by the EDAP and allows for the optimum location of the tower foundation while providing a wider shipping channel. (See Appendix E for further detail on the MTC recommendation process).

Replacement Alternatives N-2, N-6, and S-4 could accommodate any of the three variations discussed below, although the optimum locations for the main span foundations could not be provided by all replacement alternatives due to limited access to bedrock.

Cable-stayed Design

The cable-stayed design includes the use of steel cables to connect the bridge deck directly to towers. Most cable-stayed bridges have a single tower which supports both decks or separate "H" towers that support each individual deck. A single concrete vertical tower was considered for the East Span Project (see Figure 2-12 in Appendix A). Cable-stayed bridges have been used in several different countries since the 1940s. Recent examples constructed in the United States include the Sunshine Skyway Bridge in Tampa, Florida, and the Thomas Bridge in Georgia.

The cable-stayed system allows for longer spans crossing the navigational channel than could be provided with a skyway variation which requires additional piers in the channel. However, any cable-supported structure imposes additional alignment constraints. To support the two decks from a single tower, the decks of each of the parallel bridge structures must be almost parallel and at the same approximate elevation for the entire length of the main span. The main span cannot begin until each deck alignment meets these constraints. The replacement alternatives under consideration have been set to accommodate the geometric requirements for a cable-stayed main span.

The cable-stayed design variation would exceed the USCG’s minimum requirements for horizontal and vertical clearances of the main navigation opening.

The cable-stayed main span was estimated to cost approximately $100-$250 million more than the total estimated cost of an island-to-shore skyway replacement bridge.

Suspension Bridge Design (Preferred Design Variation)

The suspension design is a commonly used design for long channel crossings and has been used previously in the Bay Area on the Golden Gate Bridge and the SFOBB West Span. A classic suspension bridge has cables that are draped from towers and connected to anchorages founded on the ground at both ends of the main span. Vertical cables ("suspenders") support the bridge by connecting the draped cable to the bridge deck. While bedrock on YBI could be used for a west anchorage, bedrock is approximately 135 meters (443 feet) below the mudline for an east anchorage at the Oakland Touchdown. The use of ground-founded traditional anchorage structures at this bridge site is therefore considered less feasible and less cost-effective relative to other options.

A self-anchored suspension design variation has been identified as the preferred design variation. In a self-anchored suspension bridge, the main cables are anchored to the ends of the main span deck, eliminating the need for ground-founded anchorage structures (see Figure 2-13 in Appendix A). The self-anchored suspension design variation suspends the bridge from a steel tower. Alignment constraints for the self-anchored suspension design variation are similar to those described for the cable-stayed design variation. Decks of the bridge structures must be almost parallel and at the same approximate elevation for the entire length of the main span. The main span cannot begin until each deck alignment meets these constraints. Although a self-anchored suspension bridge looks similar to more conventional suspension bridges, it is structurally different in that it uses the bridge deck as the integral structural component that balances the force usually taken by anchorages founded on the ground. The replacement alternatives under consideration have been set to accommodate the geometric requirements for a self-anchored suspension design variation.

The self-anchored suspension design variation exceeds the USCG’s minimum requirements for horizontal and vertical clearances of the main navigation opening.

The self-anchored suspension main span was estimated to cost about $150-$300 million more than the total estimated cost of an island-to-shore skyway replacement bridge.

Skyway Design

The skyway design variation is a structure constructed of precast concrete supported by columns. With this structure type, eastbound and westbound bridges would be constructed as separate, independent structures. Under the skyway design variation, spans over the main navigation opening area could be a maximum of 150-170 meters (490-550 feet) in length. The skyway design variation would require three spans in the main span area, compared to two spans for both the cable-stayed and self-anchored suspension design variations. The skyway design does not require a complete tangent or straight section over the main span, which is needed to construct the cable-supported design variations. As a result, there could be a slight curve in the main span. An example of a skyway structure is depicted in Figure 2-14 in Appendix A.

The skyway design variation would meet but not exceed the USCG’s minimum requirements for horizontal and vertical clearances of the main navigation opening.

A skyway design variation is considered as the baseline for cost comparison purposes. A skyway span was estimated to cost approximately $90 million.

2.4 COMPARISON OF ALTERNATIVE CHARACTERISTICS

2.4.1 Funding

The base budget for the East Span Project, established in Section 188 of the California Streets and Highways Code (CSHC), is about $1.285 billion. Project funding comes from a combination of state taxes, bond revenues, and moneys collected through a one-dollar bridge toll surcharge effective January 1, 1998, on all state-owned bridges in the Bay Area. Some federal funding is also being sought for the project. State taxes, in the form of state fuel tax revenues, are 33.3 percent of the project budget, state Seismic Retrofit Bond revenues will fund 30.2 percent of the budget, and the toll surcharges from state-owned Bay Area toll bridges will fund the remaining 36.5 percent.

The legislation creating the funding mechanism for the East Span Project established the Bay Area Toll Authority (BATA) (with the same board as the Metropolitan Transportation Commission) and authorized the Authority to collect the one-dollar toll surcharge for eight years, issue revenue bonds, and allocate revenues to toll bridge projects, including the East Span Project. On June 24, 1998, through BATA Resolution No. 10, the Authority chose to extend the one-dollar toll surcharge for an additional two years beyond the eight years to fund the inclusion of specified amenities. Extension of the toll surcharge for 15 months is anticipated to generate $230 million; amenities specified in Resolution No. 10 total $141 million: $50 million for a bicycle/pedestrian path and $91 million toward the self-anchored steel suspension main span. On September 22, 1999, through BATA Resolution No. 19, the one-dollar toll surcharge was extended for an additional 0.4 months to pay for rest areas, a planning and feasibility study of a West Span bike lane, and a concept study of improvements to the Transbay Transit Terminal. The incorporation of the two resolutions results in a $1.427 billion budget for the SFOBB East Span Project.

On June 28, 2000, the Authority approved a revision to BATA Resolution No. 19 to extend the surcharge for the remaining 8.9 months permitted by statute to fund the additional costs of the Bay Bridge West Span bicycle and pedestrian study ($1,020,000) and for the remainder ($84,430,000) to be placed in a reserve account.

The total base budget of $1.285 billion includes an allocation of $80 million for a cable-supported structure. The type of cable-supported structure is not specified in the CSHC. The design options presented in Section 2.3 include cable-supported structures. Funding of a cable-supported system costing more than $80 million would require the Authority to extend the one-dollar toll surcharge beyond the initial eight-year period.

Cable-supported design variations are included in the East Span Project description of replacement alternatives. The potential visual impacts of these design options are addressed in this document.

2.4.2 Costs

Estimated total costs for each of the alternatives identified above are listed in Table 2.4-1. These costs are based on 1998 estimates and are presented in 2002 dollars. Comparative life-cycle costs are presented in Table 2.4-2. These cost estimates are conceptual and are based on available information that was available in 1998 about the existing East Span, new proposed alignments, existing utilities, historic construction costs, and quotations from various local suppliers and contractors. These estimated costs range from zero for the No-Build Alternative to $1.65 billion for Replacement Alternative N-6, suspension design option. No-Build Alternative costs do not include the $19 million interim retrofit improvements that were completed during summer 2000.

In April 2001, Caltrans published updated cost information for the Preferred Alternative (Replacement Alternative N-6, suspension bridge design option). It reflects cost increases due to such factors as increasing construction costs in a robust and competitive local economy; significant increases in the costs of steel; schedule delays which magnified the inflationary effect; and additional design amenities such as the belvederes and a wider bicycle path than is standard. Caltrans estimates that the current cost of Replacement Alternative N-6, suspension bridge option, would be $2.6 billion.

Caltrans did not prepare updated cost estimates for the other project alternatives in April 2001. However, the most significant factors contributing to increased costs would apply to all of the build alternatives.

The enabling legislation for the project, Senate Bill 60, signed by then-Governor Pete Wilson in 1997, anticipated the possible need for additional funding beyond original estimates and required Caltrans to return to the Legislature if necessary. In accordance with Senate Bill 60, Caltrans has submitted its cost estimates to the Legislature and anticipates that it will address the need for additional funding within the next few months.

Based on a comparative cost study prepared by Caltrans in 1996, it is estimated that the bridge maintenance costs for the retrofit alternative over the projected 50-year life span of the existing structure would be $44 million. A replacement structure is expected to have a service life of 150 years. Life-cycle costs of replacement alternatives have not been developed for the projected 150-year life spans of the structures. A comparison of selected maintenance operations and repairs of the first 50 years of service indicated that differences among replacement alternatives are small (see Table 2.4-2). Comparing the life-cycle costs of the replacement structure in Table 2.4-2 to the maintenance costs of the retrofit structure

Table 2.4-1 Cost Estimate Summary

 

 

Alternative

Retrofit Existing Structure

 

Skyway ($ billion)

Cable-stayed Main Span Design Variation ($ billion)

Self-anchored Suspension Design Variation ($ billion)

Alternative

 

N-2

N-6

S-4

N-2

N-6

S-4

N-2

N-6

(Preferred)

S-4

Structure and Roadwaya

0.90

1.25

1.25

1.25

1.35 - 1.45

1.35 - 1.45

1.40 - 1.50

1.45 - 1.50

1.40 - 1.55

1.45 - 1.50

Dismantle Existing East Span

N/A

0.05

0.05

0.05

0.05

0.05

0.05

0.05

0.05

0.05

Bicycle/Pedestrian Path

N/A

0.05

0.05

0.05

0.05

0.05

0.05

0.05

0.05

0.05

Aesthetic Lighting

N/A

N/A

N/A

N/A

0.012

0.02

0.012

0.015

0.02

0.015

TOTAL Construction Costb ($2002)

0.90

1.35

1.35

1.35

1.45 - 1.55

1.45 - 1.55

1.50 - 1.60

1.55 - 1.60

1.50 - 1.65

1.55 - 1.60

Source: SFOBB East Span Seismic Safety Project 30% Type Selection Report, Caltrans, May 1998.

Notes: a Cost estimates reflect the potential range in construction costs depending on skyway structure type rounded to the nearest 50 million. A haunched-concrete skyway structure is estimated to have the least cost, a uniform depth concrete skyway a mid-range cost, and a uniform depth steel structure the greatest cost.

b The cost information in this table represents the estimated cost of the various alternatives in 1998. The costs are relative to each other at the time that they were estimated. They do not represent the current costs of the alternatives, which would be greater, but still have the same relative relationship.

Table 2.4-2 Comparative Life-cycle Costsa,b ($ Million Escalated to 2002)

 

Skyway

Cable-stayed Main Span Design Variation

Self-anchored Suspension Design Variation

11

14

12

Source: SFOBB East Span Seismic Safety Project 30% Type Selection Report, Caltrans, May 1998.

Notes:

a Comparative life-cycle cost analysis estimates costs of maintenance and repair of the bridge over a projected life span (150 years) to better determine the overall bridge structure "value." A comparative analysis requires calculation of life-cycle costs of only those maintenance operations and repairs that are appreciably different for bridge design variations that are being evaluated. The table only reports costs for the first 50 years of the life span because beyond that period, it becomes increasingly difficult to make reliable estimates.

b For purposes of comparative life-cycle costs, differences between replacement alternatives were minimal.

($54 million in 2002 dollars) means that a new bridge, which would last 100 years longer, would be less expensive to maintain over the long term.

2.4.3 Constructibility

In addition to cost, "constructibility" provides a valuable comparison between the alternatives and options previously described. Constructibility encompasses the anticipated duration of construction, as well as any unusual delays, environmental issues, or risks associated with the construction process. The environmental impact issues are discussed in Section 4.14 — Temporary Impacts During Construction.

The No-Build Alternative would have no construction activity. Tasks would be limited to regular maintenance.

The Retrofit Existing Structure Alternative would include constructing two new columns in Bay waters to support the main span over the navigational channel. A total bridge closure would be necessary to connect the new columns to the cantilever section. This could be accomplished at night. During other activities, such as superstructure construction, numerous lane closures would be necessary but would be timed to minimize the impact on bridge users. Construction on the superstructure would be expected to last for the majority of the retrofit schedule, approximately six years.

The Retrofit Existing Structure Alternative is less safe for the traveling public and for Caltrans staff who will maintain the bridge during and after construction. Because there are no shoulders on the existing East Span, the construction zone for the retrofit would be highly constrained. Motorists would pass within close distances of the construction activities through the entire 4-kilometer (2.5-mile) long project, and construction equipment and workers would have to maneuver adjacent to passing traffic for the installation and removal of lane closures and other work on or above the five lanes.

Multi-staged construction and temporary detours would be required on YBI and the Oakland Touchdown area for all three replacement alternatives. Most of the construction in the Bay can be performed without affecting the existing roadways and bridge structure. The vast majority of the construction would be separated from the existing East Span. This separation would minimize traffic delays and safety hazards for construction crews, maintenance crews, and the traveling public. Caltrans is continuing to investigate lane and bridge closures to transition traffic from the existing bridge to the temporary detours and to a replacement bridge. Caltrans would plan the closures in an effort to simultaneously minimize public inconvenience, facilitate construction, and maximize public safety. The closures would be scheduled to occur during off-peak hours to the maximum extent feasible. Caltrans would implement a Traffic Management Plan to manage impacts to traffic.

A replacement alternative would also provide two standard shoulders to accommodate disabled vehicles and routine bridge maintenance activities. The replacement alternatives are expected to take five years to complete plus approximately two years to dismantle the existing structure, for a seven-year construction schedule.

2.4.4 Ability to Address the Project Purpose and Need

The No-Build Alternative would not meet the project purpose and need as described in Chapter 1 because it would not provide a lifeline vehicular connection between Oakland and YBI; would not maintain high levels of people, freight, and goods movement following an MCE; and would not correct deficiencies in design standards. The retrofit and replacement alternatives would meet the project purpose and need to varying degrees as summarized below.

The Retrofit Existing Structure Alternative would retain the vehicular connection between YBI and Oakland and would maintain the current vehicular capacity of the East Span. It would improve the seismic performance of the existing structure, enabling the bridge to withstand a seismic event, and potentially an MCE; however, it would not meet lifeline criteria. In the event of an MCE, it is anticipated that major damage to the bridge could occur. Post-earthquake repair of the bridge could require closure of the SFOBB for several months, removing the SFOBB as a transportation link and, if damage is excessive, impeding the bridge’s ability to provide emergency relief access. Replacement or repair of the bridge following an earthquake could require closure of the SFOBB for years, depending on the degree of damage.

Opportunities to improve operational safety elements of the East Span would not be possible under the Retrofit Existing Structure Alternative. The retrofit alternative would not permit changes to the existing roadway design; therefore, current roadway design standards could not be attained (see Section 1.2.3 — Current Roadway Design Standards).

Each of the replacement alternatives would continue to provide a connection between YBI and Oakland and would provide a lifeline connection between West and East Bay communities. The replacement alternatives would be constructed to withstand an MCE, providing for safety of bridge users during an earthquake. As a lifeline structure, the span would continue to provide a critical connection between San Francisco, the East Bay, and the I-80 corridor to the east. The span would provide post-earthquake transportation service for emergency response and support for the economic livelihood of the Bay Area.

The replacement alternatives would meet current roadway design standards to the maximum extent feasible. Replacement alternatives would maintain existing vehicular capacity on the East Span by providing five travel lanes in each direction, including provision of standard 3.6-meter (12-foot) wide traffic lanes and inside and outside (3-meter [10-foot]) shoulders. The replacement alternatives would also conform to current horizontal and vertical alignment, superelevation, clearance, and stopping-sight distance standards as defined in Section 1.2.3 — Current Roadway Design Standards of this report.

2.5 ACCOMMODATION OF MULTI-MODAL STRATEGIES

The SFOBB is within an important corridor of transbay travel between San Francisco and the East Bay. The bridge is currently a multi-modal highway facility that is used by public and private vehicles, trucks, buses, carpools, and vanpools. The corridor is also served by Bay Area Rapid Transit (BART), which provides rapid rail service via the submerged BART "tube," and a network of ferries.

Based on available data, approximately 36,000 people travel through the Transbay Corridor during the weekday morning peak hour in the peak direction (westbound). The following table summarizes existing person trips in the Transbay Corridor by mode:

 

Single-/Double-Occupant Vehicles

 

Carpools/

Vanpools

 

 

Buses

 

 

BART

 

 

Ferries

 

 

Total

Number of Person Trips (AM peak hour, westbound)

8,900

9,400

3,100

14,000

400

35,800

Source: Caltrans, September 1997, June 1998, and May 2000.

Because the SFOBB is a critical regional facility whose approaches are severely congested during peak periods, the feasibility of incorporating an additional high-occupancy transportation facility within the corridor (either road- or rail-based) was evaluated. The purpose of such a facility would be to increase mobility within the corridor.

Due to the scale of the project, some members of the regional community urged that congestion relief be included as part of the project purpose in addition to providing a vehicular lifeline connection. The scope of the project was not expanded to include congestion relief, because this would have resulted in lengthy public and agency debate about how best to implement a congestion relief solution. This would have caused the seismic safety component of the project to be substantially delayed. Caltrans anticipates beginning construction of this critical safety project in fall 2001. This would not have been possible if the scope of the project had included congestion relief.

2.5.1 Historical Background

Rail service was provided on the SFOBB from 1939 to 1958 by the Key System. The Key System was an electrified interurban light-rail system that utilized the south side of the lower deck of the East and West Spans of the SFOBB. It shared the lower deck with trucks and buses while automobile traffic only traveled in six lanes on the upper deck. The Key System commenced operation in 1939 and continued service until 1958. From 1939 to 1941, two other rail lines, the Interurban Electric and the Sacramento Northern, also operated on the SFOBB.

The Key System connected Oakland and Berkeley with San Francisco. The system terminated in San Francisco at the Transbay Transit Terminal where passengers could transfer to the San Francisco Municipal Railway system (Muni). In total, the Key System trains operated on 106 kilometers (66 miles) of track on the SFOBB and in the East Bay. It served the East Bay cities of Richmond, El Cerrito, Albany, Berkeley, and Oakland. The Key System also operated transbay buses.

Patronage on the Key System peaked in 1945 with 26.5 million annual passengers, with an average daily ridership of about 102,000 (including both trains and Key System buses). By 1957, ridership had declined to about 5.2 million annually (about 17,000 average daily riders). As a result of the decrease, the Key System rail lines were abandoned, and the routes were converted to Alameda-Contra Costa Transit District (AC Transit) bus service in 1958.

When Key System rail service ended, the lower deck of the SFOBB was converted to automobile use. To accommodate these changes, substantial modifications were made in San Francisco, on the SFOBB, and in the Oakland Touchdown area. New vehicle access to and from the SFOBB was constructed in San Francisco; tracks at the Transbay Transit Terminal were converted to bus lanes, and buses were rerouted onto the former rail access in the Terminal; track, ties, and other railroad facilities were removed from the lower deck of the SFOBB; and new roadways to and from the SFOBB were constructed in Oakland. Load capacity from the rail system was used to allow modern traffic loadings on the bridge, including truck traffic in any of the lanes on the top deck.

2.5.2 MTC SFOBB Rail Feasibility Study

Background

In November 1998, voters in the cities of San Francisco, Berkeley, Oakland and Emeryville passed an advisory ballot measure requesting that the feasibility of passenger rail on the SFOBB be studied by MTC. In response to this measure and general public interest, MTC studied transit service options in the Transbay Corridor, especially the possibility of rail (see MTC letter dated December 16, 1998, that was sent to the Mayors of Berkeley, Emeryville, Oakland, and San Francisco in Appendix G). Concurrently, MTC prepared two studies: a long-term capital and operating cost analysis for various transit options for the Transbay Transit Terminal, as well as a feasibility analysis of rail on the SFOBB. Because the SFOBB and the Transbay Transit Terminal are linked by function, the technical analyses conducted in each study have been coordinated and are based on shared assumptions and data.

There are two phases in the Bay Bridge Rail Alternatives Study. Phase I explored the technology options for placing rail on the SFOBB and assessed the structural feasibility and modifications that would be required for the retrofitted West Span, YBI and the new East Span of the SFOBB as currently proposed. Phase I also identified potential SFOBB rail alignments in the East Bay and in San Francisco. A final report was completed in July 2000.

The work scope for Phase II of the study will be incorporated into the Bay Crossing Study to be completed by MTC by fall 2002. MTC will study non-SFOBB transbay rail crossings, including new tubes for rail or BART, additional or expanded auto bridges with or without rail, and enhancements to existing transbay transit services, including BART, transbay buses, and ferries.

The following working papers and final report were prepared for MTC’s SFOBB Rail Alternatives Study:

These documents are available from the MTC Library, 101 8th Street, Oakland, California.

MTC Findings

Structural Feasibility and Costs. The structural feasibility of rail on the SFOBB was analyzed in the MTC study. This study analyzed four types of rail vehicles: light rail (LRT), BART, commuter rail, and high-speed rail. These vehicles vary by their loaded car weight and the rail envelope size.

The East Span replacement alternatives, as currently being designed by Caltrans, would have the structural capacity to accommodate one railroad track for LRT on the inside of each deck (north side of eastbound deck, and south side of westbound deck), four travel lanes with no shoulders, and live loads representing BART and LRT vehicle types. The MTC study found that additional strengthening beyond the established design criteria would be required if five travel lanes or vehicle types with higher live loads were desired. The placement of rail on the inside of each of the side-by-side decks limits the options for crossing YBI and connecting to the West Span. The MTC study notes that "…moving rail to the outside of the decks would provide the needed flexibility, allowing for new tunnel bores to be constructed without impacting current traffic operations."

The MTC study also observes that the feasibility of an SFOBB rail system would also be constrained by the structural requirements for rail on the West Span. The MTC structural assessment study identified two rail configurations that would accommodate rail on the West Span. Both configurations would require extensive modifications, in addition to the West Span retrofit that is currently under way. The cost for the modifications would range from $3.06 billion (Rail Suspended Below the West Span Lower Deck option) to $3.33 billion (Rail Cantilevered from the West Span Lower or Upper Decks option). These estimates include the cost of strengthening and modifying the West and East Spans to accommodate rail and four travel lanes, new tunnels through YBI, and a new tunnel or structures to Harrison Street in San Francisco. The costs do not include a structure to carry rail beyond the SFOBB Toll Plaza, structure or tunnel to the Transbay Transit Terminal in San Francisco, or costs of the rail tracks or other infrastructure to operate a rail system.

Rail Service Options. The MTC study identified four rail service options for operating rail on the SFOBB. The study notes that these options would serve different, potentially large markets but were not based on detailed analyses of demand or potential patronage.

Alternative A ­ Transbay Light Rail Service. This option, considered a modern version of the Key System, would connect the Transbay Transit Terminal with several trunk lines in the East Bay with LRT. Frequent all-day service would be provided.

Alternative B ­ BART Transbay Bridge Service. This option would take one of the existing transbay BART lines and move it to the SFOBB, expanding the capacity of BART’s peak hour transbay service. For purposes of the MTC analysis, it was assumed that the SFOBB BART would connect to the bridge via a direct connection with BART’s MacArthur station.

Alternative C ­ Basic Bridge Railroad Passenger Service. This option identifies rail service that would link the Peninsula and the East Bay via the Transbay Transit Terminal and the SFOBB. Both electrified commuter rail and high speed trains would operate on this alignment on a skip-stop "A-train/B-train" operating plan, as described in MTC’s "Blueprint" concepts for Caltrain. "A" and "B" trains would operate on 30-minute headways, resulting in 15-minute headways between major stations. In the East Bay, commuter rail trains would merge with the existing Union Pacific corridors both north and south of the SFOBB. To the north, some of the trains would extend to Sacramento as part of Capitol Corridor service. High speed rail would terminate at a new station in West Oakland.

Alternative D ­ Aggressive Bridge Railroad Passenger Service. This option is basically identical to Alternative C. However, for Alternative D, the northern "A" and southern "B" branches would extend beyond central East Bay core cities. Frequency of service would also be improved. Northbound trains would continue to Martinez with half of the trains continuing to Suisun-Fairfield. Some trains would be extended to Sacramento. High speed trains would operate over the SFOBB every 30 minutes, with every train continuing to Sacramento. The southbound commuter rail line would extend to San Jose.

Rail Infrastructure and Rolling Stock Costs. The MTC study estimated the capital costs of implementing each of the rail options, including infrastructure and rolling stock. Operational costs were not included in these estimates but they would be substantial. Total infrastructure and rolling stock cost estimates are summarized below:

Therefore, the MTC study estimated that the total cost of rail implementation, including bridge structural modifications, rail infrastructure, and rolling stock would be between $4 billion and $9 billion.

Structurally, rail is feasible on the SFOBB; however, there are numerous non-structural issues that have not been examined, such as system-wide operations, routing, costs, attaining ridership, acquiring right-of-way, and resolving environmental issues.

2.5.3 Operational Issues

This section evaluates the potential operational impacts of implementing an HOV lane or rail on the East Span.

In general, the existing East Span or a replacement span could physically accommodate an HOV lane without additional right-of-way. A replacement East Span, as currently designed, could also accommodate rail service. Rail service would require the use of one travel lane in each direction, reducing the capacity of the East Span to four travel lanes. Significant modifications to the current design would be necessary to accommodate rail service and five travel lanes.

The operational impacts on vehicular flows due to the loss of one travel lane with either multi-modal strategy are described below.

HOV Lane

An HOV lane on the SFOBB is evaluated as an extension of the existing HOV facilities at the San Francisco and East Bay approaches. Under this scenario, one of five mixed-flow lanes on the SFOBB (in both the eastbound and westbound directions) would be converted to an HOV lane. The HOV lane would be a dedicated facility for use only by vehicles with three or more people. Because right-of-way constraints on the existing or replacement East Span would preclude the use of barriers or buffers, the facility would be separated from mixed-flow traffic by striping and signing only.

An HOV lane on the SFOBB would adversely affect mobility in the Transbay Corridor, compared to the SFOBB facility without an HOV lane. During the morning peak period, the existing HOV lanes and metering signals at the SFOBB Toll Plaza operate together as a system to ensure that the capacity of the five westbound lanes on the SFOBB is maximized. As the HOV lane volume varies during the peak period, the mixed-flow metering rates are adjusted accordingly to maintain capacity flow for five lanes on the bridge. During the peak hour when the HOV volume exceeds the capacity of a single HOV lane, total vehicular capacity could be maintained if one of the five lanes on the bridge is operated as an HOV lane. The metering signals would release fewer mixed-flow vehicles as the excess HOV demand shifts into the mixed-flow lanes. However, the HOV volume before and after the peak hour would be less than the capacity of an HOV lane. Since mixed-flow vehicles would be restricted from using the HOV lane, total vehicular capacity would be less than the existing capacity as the excess HOV lane capacity would go unused. This would result in additional congestion on the approaches to the SFOBB. It is likely that the additional congestion would increase to the point of restricting access to the HOV lanes, particularly for the I-580 and I-880 approaches.

Other constraints associated with implementing the HOV lane on the SFOBB would be the result of the physical integration of the lane with existing HOV lanes, ramps, and SFOBB approaches. Substantial physical modifications, such as an HOV flyover (to connect the existing westbound HOV lanes, including the HOV flyover constructed as part of the I-880/Cypress Freeway Replacement Project, with a new HOV lane) and/or new ramps at YBI, would be necessary to minimize impacts to traffic flow operations. Therefore, costs associated with implementation of the HOV lane could be substantial and there would be no net change in person trip throughput on the bridge.

Rail

If rail on the SFOBB were implemented, one travel lane and one shoulder in each direction on the East Span would need to be converted to rail use. The loss of a traffic lane on either span would substantially impact SFOBB traffic operations. The vehicular capacity of the proposed East Span would be reduced by 20 percent. However, to accommodate rail on the existing West Span deck, it would need to occupy two travel lanes, reducing the vehicular capacity by 40 percent. This is because the West Span does not have shoulders. Consequently, the vehicular capacity of the East Span would also be reduced by 40 percent because traffic flow on the East Span would be constrained by the lowest capacity available in the corridor. As a result, about 7,300 morning peak-hour westbound person trips (4,000 vehicle trips per hour) would be displaced. (These figures are based on counts taken by Caltrans in May 2000 at the SFOBB Toll Plaza.) If this significant loss in vehicle capacity was not made up through rail ridership, it would increase the existing congestion levels on the approaches to the SFOBB for mixed-flow vehicles, as well as create delays for vehicles accessing the existing HOV facilities.

To maintain or increase the person throughput capacity of the SFOBB due to the loss of vehicle capacity as a result of rail on the bridge, the rail system must attract all of the displaced person trips (about 7,300 morning peak-hour, westbound person trips). The ability of the rail system to attract new transit trips is not solely dependent on the SFOBB segment; instead, the rail system must provide a superior mode choice in terms of travel time, convenience, cost, and reliability compared to driving. It must also not duplicate service already provided by either AC Transit, BART, or ferries. These factors would limit the number of displaced person trips to be attracted to the rail system. Further, to be successful, any new rail system would need a supporting feeder infrastructure. Rail lines, terminals, parking areas, and new bus lines would need to be developed to deliver riders to the system. Future improvements on the other existing modes would also affect new rail system ridership by providing capacity increases in the corridor. The implementation of BART’s Advanced Automatic Train Control (AATC) will allow BART to increase its capacity to 21,000 passengers during the peak hour. The AC Transit Transbay Comprehensive Service Plan calls for 140 westbound, morning peak-hour buses in the future, about an 80 percent increase over existing levels.

2.5.4 Institutional and Funding Issues

Institutional and funding issues related to implementation of either a road-based or a rail-based multi-modal strategy are summarized below.

The SFOBB is a component of the I-80 Corridor, an important corridor in the Bay Area for commute travel, freight movement, and recreational travel. It has been studied extensively by regional planning organizations such as MTC and local transit agencies. These studies include:

These studies identified existing and future system deficiencies and travel demand and evaluated improvement strategies, such as HOV lanes, improved ferry service, LRT corridor identification, and commuter rail service. None of these studies has identified an HOV lane or a rail-based system on the SFOBB as a preferred improvement strategy, although AC Transit has requested that Caltrans study an HOV lane on the SFOBB. Caltrans evaluated such a facility in October 1994. The MTC SFOBB Rail Feasibility Study identified preliminary estimates of the cost of SFOBB rail, structural modifications to the East and West Spans, and possible service operating scenarios. The study did not estimate potential ridership or identify environmental constraints.

Because none of these studies has identified an HOV lane or rail on the SFOBB as a preferred strategy, neither of these multi-modal strategies has been included in either the Track 1 or Track 2 project lists of the MTC’s 1994 RTP or its 1996 and 1998 updates, including a 1999 amendment. The planning horizon for the RTP is 20 years. MTC could include the multi-modal strategies in subsequent RTPs if the projects are consistent with local and regional objectives and strategies for congestion management. In addition, neither multi-modal option was included in a recently enacted statewide funding package for transportation improvements (Governor’s Traffic Congestion Relief Program [TCRP], July 2000).

No cost estimates have been prepared for implementation of an HOV lane on the SFOBB but they would likely be less than rail. Costs may include modifications to existing ramps or construction of new ramps; these costs may be substantial.

The construction and operation of the facilities required to implement an HOV lane or rail system would require additional funding and sources of funding beyond those committed to the East Span Project. Replacement bridge types and amenities for which funding has been allocated by state legislative action do not include construction of HOV or rail systems (see Section 2.4.1 — Funding). Other local, regional, state, and federal sources fund multi-modal projects. However, since costs to build, operate and maintain the existing local and regional transportation system exceed available transportation funding sources by $7 billion over the next 20 years, it is assumed that existing sources of revenues would remain committed in the foreseeable future to support existing transit services and expenditure priorities. Commitment of new potential funding and funding sources for multi-modal projects on the SFOBB will depend on the political and economic environment in the future.

The East Span Project’s purpose is to provide a seismically upgraded vehicular crossing between YBI and Oakland. Although multi-modal strategies were evaluated as part of the alternative definition process, no multi-modal strategies are within the purpose and scope of the SFOBB East Span Project.

The East Span Project would maintain the current vehicular capacity of the existing East Span. The implementation of any multi-modal strategy on the SFOBB would be subject to independent evaluation and funding as a separate project in the future. Not all rail systems could be accommodated by the East Span Project without significant modifications to the currently proposed design; however, the East Span Project does not create any additional obstacles to implementing a rail project, or other technologies, in the Transbay Corridor in the future.

The near-term implementation of either a road- or rail-based high-occupancy transportation multi-modal strategy would be constrained by several factors. Planning, funding, and implementing new transit services, which would be integrated with the existing transportation system in the Bay Area, would take substantially longer than the East Span Project would take to build. Implementing an HOV lane or rail-based transit facility on the East Span without additional infrastructure improvements, such as grade-separating structures or barriers, would adversely impact traffic operations on the approaches at either end of the bridge.

2.6 CONSTRUCTION ACTIVITIES

Similarities Between Construction of Alternatives

The retrofit and replacement alternatives have similar construction issues with respect to scale of work, in-water construction, and extent of laydown areas on YBI and the Oakland Touchdown area.

Scale of Work

Construction of the retrofit and replacement alternatives would require use of large-scale construction equipment and would involve labor-intensive construction activities. Noise emitted from driving large piles would be similar for the retrofit and replacement alternatives. The construction period for all build alternatives is anticipated to be approximately 6-7 years, including dismantling of the existing bridge under the replacement alternatives.

In-Water Construction

For all build alternatives, barges would be used for material delivery, dredging, drilling, pile driving, lifting, pile extraction, constructing cofferdams, and dismantling. Special barges and lifting equipment would be used to accommodate heavy equipment needed to support large-scale pile drivers. In areas of shallow water, some construction would take place from trestles and barges, and in deeper water, construction would take place from barges.

In-water construction activities would have similar impacts on the movement of commercial vessels and recreational boats, which would be diverted from construction areas. The main navigation opening near YBI would remain open during construction. The width would be reduced during construction, but not less than the minimum width required by the USCG.

Dredging would be required for portions of both the retrofit and the replacement alternatives for excavation, for cofferdams, and to accommodate barge access because some locations have water depths that are shallower than the draft of a barge. The anticipated maximum draft for the barges is 3 meters (10 feet). To ensure adequate clearance over potential irregularities in channel depth, to allow for some potential resettlement of materials in the channel after dredging and ""listing of barges during heavy lifts, the channel would be dredged to a depth of 3.6 meters (12 feet) adjacent to the Oakland Touchdown and 4.3 meters (14 feet) for the rest of the access channel. Dredging to a depth of 4.3 meters (14 feet) would also be required northeast of the USCG facility on YBI for Replacement Alternative S-4.

Construction Staging Areas on Yerba Buena Island and Oakland Touchdown

Construction laydown and access areas would be needed on YBI and at the Oakland Touchdown area for construction storage and staging. The entire eastern end of YBI would be required, except for Building 262 and the structures and some landscaped areas in the Senior Officers’ Quarters Historic District. A dock and vessel mooring facility would be constructed near the Parade Grounds and/or offshore from the eastern end of the island to facilitate the delivery of material and equipment from barges. Access to the Oakland Touchdown construction area would most likely be from surface streets located south of I-80, such as Burma Road.

2.6.1 Retrofit Existing Structure

Retrofit construction would require large-scale construction equipment and labor-intensive construction activities. Equipment used for construction of the retrofit would include delivery trucks, cranes, barges, dredges, pile drivers, concrete mixers, batch plants, cofferdams and forms, excavators, backhoes, and manual equipment to remove rivets and add bolts. The sequencing of work would depend largely on the contractor, but it is anticipated that construction activity would not be in progress concurrently along the entire length of the existing bridge. Construction is estimated to require six years to complete.

A possible construction scenario for the retrofit alternative is summarized below. Activities are described for three distinct construction areas: YBI, the Oakland Touchdown area, and in the Bay. Additional information on construction activities, impacts, and avoidance and minimization measures can be found in Section 4.14 — Temporary Impacts During Construction Activities.

Yerba Buena Island

Equipment, materials, and work crews would be transported to YBI by motor vehicles and/or barges. Contractors would require construction laydown and access areas on YBI to retrofit the YBI East Viaduct and retrofit Columns YB2 through YB4 and E1 (Figure 2-4.1 in Appendix A) and for construction storage and staging for the entire retrofit. The contractor would be responsible for arranging additional space requirements. It is anticipated that, except for Building 262 and the structures and some landscaped areas in the Senior Officers’ Quarters Historic District, all open spaces on the eastern end of YBI would be required for construction staging. Construction activities on YBI are expected to include soil and rock removal to expand and supplement footings for columns on the island and to install concrete enclosures for the towers at Columns YB2, YB3, and YB4.

Oakland Touchdown Area

No retrofit activities are anticipated in this area because retrofit work was completed for bents east of Bent 22 in March 1998. However, portions of the Oakland Touchdown area may be used for construction staging, equipment storage, and parking for work crews.

In the Bay

Construction in the Bay would take place from barges and/or trestles. Substructure (below bridge deck) activities would consist primarily of expansion of existing footings, pile caps, and columns, which may require removal of some existing material such as concrete. In areas of shallow water at the Oakland Touchdown, cofferdams would need to be constructed to provide work access at each column where foundations are being expanded. Dredging would be required to provide an access channel in shallow water for barges. Dredge quantities for the retrofit alternative are shown on Table 4.14-4. In areas of deeper water, prefabricated pile caps would be used to retrofit the columns.

Tower strengthening would be required to minimize the damage or instability that would occur during a large earthquake and to reduce displacements at the top of the tower to manageable levels. This would be achieved by encasing either whole towers or tower members in concrete. The steel towers at Columns YB2, YB3, and YB4 would be completely encased in concrete; the steel members of the towers at Columns E6 to E8 and E10 to E22 would be encased in concrete.

All foundations, except for that of Column E9, would also be strengthened to reduce and manage the displacement of the foundations.

At Columns YB2 to YB4, cast-in-drilled-hole concrete piles would be used to surround the existing spread footing foundations. The new pile caps would enclose the modified footings.

The existing timber pile foundations from Columns E6 to E16 would be strengthened and stiffened by installing a total of 44 large capacity 1.5-meter (5-foot) diameter cast-in-steel shell pipe piles around each existing column footing. A reinforced and prestressed concrete pile cap would fix the top of the new piles and surround the existing column to strengthen it and connect it to the new piles.

The existing timber pile foundations from Columns E17 to E23 would be strengthened and stiffened by installing a total of 36 large capacity 1.5-meter (5-foot) diameter steel pipe piles at the north and south ends of each existing column footing. A reinforced and prestressed concrete pile cap would fix the top of the new piles and surround the existing column to strengthen it and connect it to the new piles.

In addition, two new columns, E2A and E2B, would be constructed to support the existing cantilever structure (see Figures 2-4.1 and 2-4.2 in Appendix A). The towers for the new columns would be constructed of concrete and would be approximately 30 meters (98 feet) tall. The large diameter steel pipe piles for the new columns would need to be driven deep into the Bay mud to be founded on stable bearing materials. For Column E2B, the distance to bedrock would be nearly 91 meters (300 feet) below Mean Low Water (MLW). Construction of the new columns would require large-scale construction equipment to drive large-diameter piles, approximately 3 meters (10 feet) in diameter, into stable Bay bottom sediments or rock. Pile drivers would be mounted on deep-draft barges.

It is anticipated that retrofit activities in shallow-water areas near the Oakland Touchdown would be conducted from barges and temporary trestles constructed adjacent to the existing East Span. Dredging would be required to provide barge access in locations where the water depth is shallower than the draft of a barge.

Superstructure

Retrofit of the superstructure would include any construction on or above the lower roadway deck. Isolation bearings would be installed on top of the towers at the connections to the steel truss superstructure. Many of the truss elements adjacent to and above traffic would be strengthened and stiffened. Cross members of the truss would be strengthened or stiffened by adding steel plates, replacing rivets with high-strength steel bolts, and replacing lattice members with solid members or plating them.

A steel space frame (external edge truss) may also be used to strengthen portions of the cantilever section. These frames would extend from the top roadway deck to the lower roadway deck. In addition to the space frame, elements of the cantilever truss at the top would be removed to help isolate each of the cantilever segments from each other.

2.6.2 Bridge Replacement Alternatives

Construction of any of the replacement alternatives would require use of large-scale construction equipment, but because numerous pre-cast materials would be used with a replacement alternative, construction activities would not be as labor-intensive as with the Retrofit Existing Structure Alternative. The replacement alternatives are expected to take five years to complete plus approximately two years to dismantle the existing structure, for a seven-year construction schedule. Traffic would be diverted onto the new structure before the existing bridge is removed. As a result, seismic safety and lifeline criteria would be achieved for westbound traffic four years after the start of construction and, for eastbound travelers, five years after the start of construction.

Possible construction scenarios for a replacement alternative are summarized below. Activities are described for three distinct construction areas: YBI, the Oakland Touchdown area, and in the Bay. Additional information on construction activities, impacts, and avoidance and minimization measures can be found in Section 4.14 — Temporary Impacts During Construction Activities.

Yerba Buena Island

Temporary Construction Easements. The land within the existing easement held by Caltrans on YBI would be insufficient for all of the project’s staging and construction area requirements. While the contractor would be responsible for arranging additional construction space requirements, it is anticipated that all open spaces on the eastern end of YBI would be required for construction staging, except for Building 262 and the structures and some landscaped areas in the Senior Officers’ Quarters Historic District. A portion of the northern temporary detour would be built in landscaped areas of the Historic District. The Parade Grounds would be used for temporary administrative offices (trailers), parking, maintenance, equipment and material storage, and related activities.

Arrival of Material and Work Crews. Equipment, materials, and work crews would be transported to YBI either by motor vehicles or by barges. Trucks would use Macalla Road to deliver materials. Materials delivered by truck, during non-peak traffic hours, if feasible, may include cement, reinforcing steel, prestressing steel, structural steel for the temporary detours, falsework material and form lumber. Barges would be used to deliver larger structural segments of the bridge (piles for the tower and structural steel for the tower and main span deck). Cranes situated at locations within the temporary construction easement and/or contractor-leased work areas on the island would be used to lift materials into place. Also, some material trucked to YBI would be loaded onto barges and barged to construction sites along the bridge.

Mobilization/Grading. Grading would occur in the area surrounding the temporary detours and new structures, the Parade Grounds, and hillside areas to provide access for cranes, delivery vehicles, and other construction. Some of the most extensive grading would probably occur where the contractor is creating access to build footings for the temporary detours and the permanent structures. The graded area around the new span would need to be a minimum distance horizontally from the structure to provide adequate vertical clearance for cranes and other equipment.

Soil and rock removal would be required up slope on the island near the tunnel portal in preparation for temporary detour and transition structures, a maintenance garage, a power substation, and construction of footings for columns on the island. Graders, backhoes, loaders, excavators, dump trucks, hoe rams, compactors, survey equipment, sieves, water trucks, concrete trucks, and cranes would be used to complete this task. For the temporary detour footings positioned on hillside areas, sheet pile and/or other temporary shoring may be used to stabilize excavated areas of slope; and cement-modified soil backfill may be used to stabilize the foundations of the transition structure.

Roadway Modifications. Several roadways on YBI would require modifications as a result of construction of the new East Span. Figure 2-20 in Appendix A depicts the existing configurations of the roadways and also shows the modifications to existing roadways (represented by shading). The modifications shown are for Replacement Alternative N-6. The other replacement alternatives would require similar roadway modifications, but the vertical and horizontal changes to the roadways would be slightly different, depending on the bridge alignment.

Macalla Road would be lowered about 1 meter (3 feet) at the intersection of Southgate Road and Macalla Road. The lowered Macalla Road would conform back to the existing grade 75 meters (246 feet) up slope and about 60 meters (197 feet) down slope. The Macalla Road hairpin at the Southgate Road intersection would be shifted about 5 meters (16 feet) towards the inside of the curve.

Once the eastbound temporary detour is constructed, Southgate Road would be closed to public access for approximately 20 months. As a result, direct access from one side of the bridge to the other, east of the tunnel, would be eliminated during this period. Access from one side of the island to the other side would be via Hillcrest Road and Treasure Island Road. Vehicles traveling to or from San Francisco on the south side of the island would make a U-turn at the Hillcrest Road/Macalla Road intersection.

Before Southgate Road is re-opened, it would be realigned both horizontally and vertically and the lanes would be upgraded to standard width. It is expected that Southgate Road would be shifted approximately 13 meters (43 feet) east at its greatest divergence from the existing alignment, and the roadway would be lowered up to 3 meters (10 feet) from the existing roadway profile for all replacement alternatives. The modification would be made because the existing roadway is located where new columns and abutments would be placed.

In addition, construction of the eastbound temporary detour would require closure of the eastbound off-ramp and the westbound on-ramp on the east side of the YBI tunnel for approximately three years. Access to the SFOBB would continue through the use of the ramps at Hillcrest Road on the west side of the island. The intersection of Treasure Island Road and Southgate Road serves traffic exiting the bridge onto Yerba Buena Island on the east side of the tunnel. A temporary intersection would be constructed south of the existing intersection to serve this traffic and would require a temporary road through an existing slope approximately 35 meters (115 feet) south of Building 206 and Quarters 8.

In consultation with the USCG, the USCG road would be permanently realigned to avoid the columns of the new bridge. For each replacement alternative, the realigned road would be configured differently to avoid different column locations. The section of the USCG road that is roughly parallel to the existing bridge would be shifted south. A new gate and guard shack would be constructed for the realigned road. The access road from the USCG road to the parking lot would be moved from its present location northeast toward the access gate. This temporary access road would be in place for most of the construction period.

A portion of the access road to Building 262 would be modified in two phases (once to avoid the footings of the eastbound temporary detour and, ultimately, to avoid columns of the new bridge). The road would be modified for each replacement alternative but would be configured differently to avoid different column locations. While the eastbound temporary detour is in place, the road would be temporarily realigned approximately 50 meters (164 feet) south of the existing road (see Figure 2-20 in Appendix A). A portion of the access road leading to Building 262 would be permanently realigned approximately 15 meters (49 feet) to the south and would become a two-lane roadway that would conform to the existing single-lane dirt road approximately 115 meters (377 feet) from the eastern end of YBI.

Support Construction. A dock may be constructed on the north side of YBI near the Parade Grounds to facilitate the loading and offloading of material from barges and/or one other temporary barge dock would be constructed under the main span and adjoined to the eastern end of YBI near Building 262. Support facilities such as a maintenance garage and power substation would be constructed.

Construction of Temporary Detours and New Span. A summary of the staging sequence on YBI follows.

The temporary detours would be operational for approximately two years. The period from the beginning of construction to the end of dismantling would be approximately four years. The detours may be removed as soon as they are no longer needed to carry traffic or they may be removed as one of the last steps of bridge construction on YBI, because the contractor may use them as platforms from which to construct other portions of the bridge.

New footings, new columns, and retrofitting and widening the East Viaduct would require drilling, forming, excavation, backfilling, driving piles or tie-downs, erecting steel, placing reinforcing steel, placing concrete, and constructing concrete forms. The majority of excavation would be conducted to provide access to construct the footings. Falsework would be constructed underneath the cast-in-place-concrete structures until those structures are self-supporting. Concrete might be mixed at a batch plant located either on the island or remotely. Trucks would deliver concrete to the site, and it would be poured or pumped into place. Cranes would be used for steel erection, lifting forms, placing reinforcing steel, and raising materials and equipment to locations on top of the structure.

For construction of Column W2 with a northern alternative, substantial excavation and bedrock removal would be necessary to reach the elevation of the footing. The exterior of the column would be concrete, and the interior of the column would consist of four pre-cast shell tubular units that would be filled with concrete. The tubular units would arrive on a barge via Clipper Cove and be lifted into place by crane. The bent cap atop this tubular unit would be a cast-in-place concrete box girder.

The columns for the transition structures would be cast-in-place concrete, and the deck would be a cast-in-place post-tensioned box girder. Pile drivers would be used to drive the steel H-piles that would be used for most of the footings.

Oakland Touchdown

Temporary Construction Easements. As is the case on YBI, the right-of-way available for staging operations would not be sufficient for constructing the new structure. Land adjacent to the Caltrans right-of-way on the south side of the existing roadway would likely be required for construction staging. While the amount of area has yet to be determined, it is likely the construction yard/easement would occupy 1-4 hectares (2.5-10 acres).

Arrival of Material and Work Crews. Access to the site would most likely be from I-80 and surface streets south of I-80, such as Burma Road. As the bridge is being built westward, the contractor may build a trestle out to the first skyway column for the delivery of materials, equipment, and work crews.

Roadway Modifications. The existing Caltrans maintenance road has been redesigned and would cross under the eastbound roadway at a point east of the existing undercrossing. This location was selected to minimize the amount and impact of fill in the Bay and yet provide enough overhead clearance for vehicles to cross under the eastbound roadway (see Figure 2-25 in Appendix A).

Construction of Temporary Detours and New Span. As the new eastbound approach and bridge structures are completed for all replacement alternatives, traffic would be re-routed from the existing structure to the new structure through the use of a temporary roadway (see Figure 2-25 in Appendix A and Section 2.6.4 — Temporary Detours on Yerba Buena Island and Oakland Touchdown Area for more detail).

Construction activities for all replacement alternatives in the Oakland Touchdown area would primarily consist of paving, traffic maintenance, excavation of buried rubble, riprap and footings, drilling, settlement control measures, removal of some existing roadways, construction of temporary access trestles, and dredging in shallow water to provide barge access to the shoreline of the western edge of the Oakland Touchdown area.

Pile driving and placement of footings in the water adjacent to the Oakland shoreline would be required to build new bridge structures. This would require the use of equipment from land, trestle, and/or barge as described above. For Replacement Alternatives N-2 and N-6, the structures would encroach into existing sand flats and eelgrass beds and land-based roadways would be constructed on imported engineered fill. For all replacement alternatives, excavation of the area would occur for the construction of footings and pile driving and would include removal of buried fill or riprap that extends east from the westbound abutment. A riprap shoreline, replacing the existing riprap, may be constructed along the edge of the new alignment near the existing shoreline where the bridge elevation is approximately 5 meters (16 feet) above MSL.

There is the potential for soil settlement in the Oakland Touchdown area because the soil/fill is underlain by soft materials. For Replacement Alternatives N-2 and N-6, wick drains and a surcharge would be used to accelerate the consolidation process of the new embankment fill, some of which would be cellular concrete. Other design considerations such as compaction may also be used to reduce the risk of unacceptable settlement. Any permanent fill placed, except for cellular concrete, would be compacted to Caltrans specifications.

For Replacement Alternatives N-2 and N-6, a portion of the westbound lanes to the east of the bridge abutment would encroach on the Bay, requiring use of engineered fill. A portion of the Caltrans maintenance road located to the west of the bridge abutment would also require use of engineered fill.

In the Bay

Arrival of Material and Work Crews. Employee and equipment access would be by boat, barge, the replacement bridge, or temporary trestle. Vessels used for delivery of workers, equipment, and materials should be able to moor at the end of the temporary docks at YBI or on trestles at the Oakland Touchdown area.

General Construction Information. Most in-water construction would take place from barges or from the decks of the skyway as it is being built outward into the Bay. Barges would be used for material delivery, dredging, drilling, pile driving, lifting, possibly concrete batch plants, and dismantling. Special barges and lifting equipment would be used to accommodate heavy equipment needed to support large-scale pile driving. In areas of shallow water, trestles could be used in conjunction with barges. It is expected that the trestles, if used, would provide five working platforms (approximately 12 meters [39 feet] in width) around columns near the Oakland Touchdown to support lighter equipment.

Dredging. Dredging would be required for portions of the Retrofit Existing Structure Alternative and each replacement alternative for barge access, foundation construction, and pile cap construction because near the Oakland shore the water depths are shallower than the draft of a standard barge. The proposed access channel for barges would be on the north side of the northern alternatives and the south side of the southern alternative. The anticipated maximum draft for the barges is 3 meters (10 feet), but to ensure adequate clearance over potential irregularities in channel depth, barge ""listing during heavy lifting, and to allow for some potential resettlement of materials in the channel after dredging, the channels would be dredged to a depth of 3.6 meters (12 feet) adjacent to the Oakland Touchdown and 4.3 meters (14 feet) for the rest of the channel. Dredging to a depth of 4.3 meters (14 feet) would also be required northeast of the USCG facility on YBI for Replacement Alternative S-4. Barge anchor lines would be moved into position from smaller boats as opposed to the primary barge(s) to prevent the dragging of anchors into position, and barge anchor lines would be kept taut as the tide and levels change in order to minimize contact between the lines and the Bay bottom.

Section 4.14.10 — Temporary Impacts, Construction Excavation, and Dredging discusses dredging and options for disposal of dredged materials in more detail. Estimated dredged quantities for the build alternatives are presented in Table 4.14-4. Figures 2-21 and 2-22 (in Appendix A) illustrate the potential barge access channel configurations denoted by the dredging limits at the Oakland Touchdown and YBI.

Structure Construction. The substructure (below the tops of the columns) would consist of columns, foundations, piles, pile caps, anchoring systems, fenders, navigation electrical systems, and possibly a corrosion monitoring system. Substructure construction would consist primarily of installation of columns, piles, and pile caps. It is expected that cofferdams would be constructed to build columns in shallow water near the Oakland Touchdown, and cast-in-steel shell piles would be driven to serve as the foundation to the permanent columns. Where piles are driven, mud within the piles would be removed and replaced with concrete placed by pump. The removed mud would be beneficially reused or disposed of off-site. Construction of columns adjacent to YBI, including the main span tower, would require Bay bottom rock removal to secure the tower foundation. Excavation would occur to remove loose rock, which would be disposed of off-site at an upland location. Shafts would then be drilled through the bedrock down to and into the load-bearing strata and piles would be driven into the shafts. Construction of the main span tower and columns would require large-scale construction equipment, including cranes, barges, dredges, drill rigs, concrete batchers, and concrete pumps. Pile drivers and drills would be mounted on deep-draft barges to drive large-diameter piles as required.

The superstructure (the portion of the bridge above the top of the columns) would be primarily constructed of steel and concrete and would consist of girders, cable elements, the deck, deck joints, barriers, bearings, lighting, and signing. Many of these items would be pre-cast or fabricated off-site then transported to the site and lifted from barges using floating and tower cranes. For a portion of the main span, the superstructure would be delivered to YBI, set on the shore and lifted with land cranes. Barge-mounted concrete batch plants may also be used to pump concrete into forms suspended over water for the bridge deck at both the east and west ends of the project. A temporary structure would be built from YBI east into the Bay to support the main span while the permanent bridge deck and main tower are constructed. Temporary columns may be placed in the Bay or on either side of the permanent main tower. Temporary trestles may be constructed from the Oakland Touchdown westward.

Once portions of the new structure are constructed, they could be used as working platforms for other construction activities. Construction activities taking place from the new structure could include delivery of materials and equipment and lifting and positioning of structural components.

For construction of the main tower, Bay bottom sediments would be removed, holes would be drilled into bedrock, and hollow steel piles would be driven or socketed into the holes. A prefabricated steel box pile cap would be floated into position and sunk onto them, sealed around the piles, and pumped dry. The pipe piles and pile cap would be filled with reinforced concrete and steel creating a surface on which four prefabricated tower legs would be erected. The legs would be raised by cranes and bolted together by link beams.

For the main span, prefabricated steel deck segments would be transported to the site by barges, raised by crane, and placed on falsework. Each newly elevated segment would be slid forward on the falsework and connected to the previously installed segment. After the cables and suspenders are anchored to the deck, the falsework would be removed and utilities would be installed.

Construction of the skyway piles would be similar to that of the main tower. The piles would be driven into the Young Bay Mud, a prefabricated steel box pile cap would be floated into position and sunk onto the piles, sealed around them, and then pumped dry. Precast concrete fenders would be brought to the site and attached to the pile cap. The pipe piles and then the pile cap would be filled with reinforced concrete, creating a surface on which the columns can be founded.

Bridge Closures. Caltrans is continuing to investigate lane and bridge closures to transition traffic from the existing bridge to the temporary detours and to a replacement bridge. Caltrans would plan the closures in an effort to simultaneously minimize public inconvenience, facilitate construction, and maximize public safety. The closures would be scheduled to occur during off-peak hours to the maximum extent feasible. Caltrans would implement a Traffic Management Plan to manage impacts to traffic.

2.6.3 Dismantling the Existing SFOBB East Span

Dismantling the existing SFOBB East Span would be required to provide land connections to the new span for replacement alternatives at YBI and the Oakland Touchdown area. USCG also requires removal of the entire existing bridge for the safety of marine traffic once a replacement bridge is constructed. The Coast Guard Bridge Administration Manual, Commandant Instruction M16590.5A, requires "that any part of bridges which are replaced (except those parts incorporated into the new bridge) be removed down to the natural bottom of the waterway…" (See U.S. Coast Guard [USCG] letter dated August 12, 1998, in Appendix G.) The USCG currently plans to require that existing bridge piers and temporary pier piles be removed to an elevation of at least 0.46 meter (1.5 feet) below the mudline, to be measured at the time of removal.

The existing bridge, access trestles, temporary falsework, and temporary detours would be removed under the replacement alternatives. The methods of removal selected by the contractor would comply with all dismantling guidelines of the following required permits: Section 401 of the Clean Water Act, a National Pollutant Discharge Elimination System (NPDES) permit, an ACOE permit pursuant to Section 10 of the Rivers and Harbors Act, a USCG permit pursuant to the General Bridge Act of 1946 and a Bay Conservation and Development Commission (BCDC) Major Permit.

Removal would be conducted in such a manner that the portion of the structure not yet removed remains in a stable condition at all times.

There are two primary physical constraints affecting the dismantling task. First is the proximity of the replacement alternatives to the existing spans, which would necessitate performing most marine activities from one side. Second, the shallow water depths beneath the spans as they approach the Oakland Touchdown area would require using shallow-draft barges or dredging along one side and underneath for deeper draft barge access.

Dismantling activities would consist of seven major stages, which represent major components of the bridge (see Figure 2-15 in Appendix A):

The YBI viaduct, the YBI shallow truss approach spans, the Oakland shore section, and the YBI temporary detours would be dismantled during construction of a replacement alternative because of construction staging. The three other sections would be dismantled under separate contracts.

Dredging. Some areas near the Oakland Touchdown are too shallow to accommodate the large barges needed to complete the dismantling process; thus, an access channel would need to be dredged. Once the superstructure is removed, the bridge foundations would be removed to an elevation of at least 0.46 meter (1.5 feet) below the mudline. This would require the excavation of sediments around the footings using cofferdams and techniques such as reverse circulation drilling, jetting, and air lifting to remove the material around the footings. These methods involve creating a slurry of material within the cofferdam and lifting or pumping it into the drilling vessel or barge. The material may also be removed by mechanical clamshell excavation; however, dustpans and sidecasters would not be permitted. Access dredging for dismantling and sediment reuse/disposal options are described in Section 4.14.10 — Temporary Impacts, Construction Excavation, and Dredging and the Dredged Materials Management Plan (DMMP) (see Appendix M).

Superstructure

Removal of deck structures could be performed by cutting them into pieces or by disassembling them panel by panel. Steel truss spans over the water near the Oakland shore cannot be removed by conventional barge and crane methods due to the shallow water and low clearance under the deck. A possible option is to construct temporary supports under the span and disassemble the truss segment by segment. Other possible methods to remove the steel trusses include dredging for barge clearance, constructing access embankments of temporary engineered fill, or using special shallow-draft barges or rigging devices for lowering sections onto barges from the bridge deck. Protective measures would be taken to prevent materials or debris from falling into the Bay. Depending on location, materials could be removed by barge or truck to a predetermined site for reuse, recycling, or disposal. Depending on methods used by the contractor, the temporary detours on YBI (described in Section 2.6.4 — Temporary Detours on Yerba Buena Island and Oakland Touchdown Area) could be designed for simple erection and disassembly with relatively light equipment. Access dredging for dismantling and sediment reuse/disposal options are described in the DMMP (see Appendix M).

Substructure

Large structural elements could be lifted from their bases in one piece or piece by piece. Dismantling of the concrete foundations at the columns would require reducing the reinforced concrete to pieces that are small enough to be hauled away. This could be done by mechanical means such as saw cutting, flame cutting, mechanical splitting, or pulverizing and hydro-cutting. According to ACOE and BCDC, another acceptable method of disposal would be to use the hollow interiors of the columns remaining below the mudline as receptacles for pieces of concrete. As the upper portion of the column is dismantled, pieces of concrete could fall into the hollow interiors below the mudline. When the portion of the column above the mudline is completely removed, the column remaining below the mudline could be capped or would gradually fill in through siltation. Removal of the columns to 0.46 meter (1.5 feet) below the mudline could be done by an underwater dismantling method or by constructing cofferdams at each column. The cofferdam method includes construction of a cofferdam around the column, pumping the water out, and removal of concrete with jackhammers, concrete saws, drills, corers, and cranes to lift the debris out. Depending on methods used by the contractor, cofferdams may or may not be used for columns adjacent to YBI and the Oakland Touchdown. Use of cofferdams is assumed for purposes of estimating dredge disposal quantities generated by existing bridge removal (see Table 4.14-4). Any reinforcing steel would be cut off to remain flush with the face of the concrete that remains below the mudline.

2.6.4 Temporary Detours on Yerba Buena Island and Oakland Touchdown Area

Temporary detours are designed to reroute traffic around the existing structure on YBI and at the Oakland Touchdown area.

Several temporary detour options were considered for YBI and evaluated based on construction feasibility, impacts to YBI resources, construction schedule impacts, traveler and worker safety, and traffic operational impacts. It was determined that the preferred option for temporary detours would be a north-south detour option. This option is discussed below. Other options considered and withdrawn are presented in Section 2.7.10 — Temporary Detours.

Yerba Buena Island

On YBI, the temporary detours would route traffic around the construction area while portions of the existing East Span are demolished and new transition structures are completed where the existing bridge now stands. The temporary detours would allow the replacement structures to be connected to the retrofitted YBI East Viaduct while minimizing impacts to traffic.

Replacement Alternatives N-2 and N-6, North-South Temporary Detour Options. Replacement Alternatives N-2 and N-6 temporary detour options are located entirely on land and range in length from 480 meters (1,574 feet) to 580 meters (1,902 feet).

The westbound temporary detour would be constructed north of the YBI transition structure and existing East Span. Westbound traffic would be routed from the new westbound bridge structure onto the temporary detour, to the existing viaduct, then to the existing YBI tunnel. The eastbound temporary detour would be constructed south of the transition structure and existing bridge (see Figures 2-16.2 and 2-17.2 in Appendix A). Eastbound traffic would exit the tunnel onto the eastbound temporary detour and connect to the lower deck of the modified existing bridge which would continue to carry eastbound traffic during construction. In order to allow for eastbound traffic to travel from under the existing westbound (upper) deck, a cast-in-place concrete portal frame would be constructed to support the south edge of the westbound deck. When the load is being transferred from the support columns to the portal frame, the eastbound and westbound traffic lanes would be fully closed, allowing for removal of the columns.

Replacement Alternative S-4 North-South Temporary Detour Option. Replacement Alternative S-4 temporary detour would range in length from 400 meters (1,312 feet) to 450 meters (1,476 feet).

Replacement Alternative S-4, north-south temporary detour, would require placing three temporary columns immediately offshore from YBI. The westbound temporary detour would be constructed north of the transition structure and existing bridge. Westbound traffic would be routed from the existing viaduct to the temporary detour, then back onto the existing East Span before the tunnel. The eastbound structure would be placed south of the transition structure and existing East Span (see Figure 2-18 in Appendix A). Eastbound traffic would exit the tunnel, transfer to the eastbound temporary detour, and connect to the new eastbound bridge.

Oakland Touchdown Area

Temporary detours would be built on engineered fill on existing land. Temporary construction easements would be required where the temporary detour limits extend beyond the existing rights-of-way.

Temporary detour roadways at the Oakland Touchdown area would be similar for the northern replacement alternatives. The eastbound temporary detour roadway would be constructed to the south of the existing eastbound lanes, requiring relocation of the existing Caltrans maintenance road and use of Port of Oakland land. Temporary roadways would not be required for construction of the westbound approach and structures. Construction sequencing would begin with the construction of the westbound approach roadway and rerouting westbound traffic from the existing westbound approach onto the new westbound structure. Following construction of the eastbound approach and structure, eastbound traffic would shift from the temporary detour onto the new structure, and the Caltrans maintenance road would be realigned.

Under Replacement Alternative S-4, traffic would remain on the existing East Span until completion of the new westbound and eastbound structures. Once the eastbound structure is completed, eastbound traffic would be diverted from the existing bridge to the new eastbound structure and onto a temporary detour roadway on existing Port of Oakland land south of the proposed structure. Westbound traffic would remain on the existing structure until construction is completed for the westbound structure and approach. On completion of the westbound bridge approaches, roughly between stations 87 and 89 on Figures 2-11.4 and 2-11.5 (Appendix A), westbound traffic would be diverted to the new westbound structure.

2.7 ALTERNATIVES CONSIDERED AND WITHDRAWN

In addition to the alternatives and project features described above, Caltrans considered a range of other project alternatives and features prior to the DEIS which were ultimately withdrawn from further consideration for a variety of reasons. These alternatives (shown on Figure 2-19 in Appendix A) and features are described below, along with the reasons for their withdrawal.

2.7.1 Replacement Alternative N-1

Replacement Alternative N-1 is a 3,685-meter (12,087-foot) long replacement alignment located to the north of Replacement Alternative N-6. Eastward from the YBI tunnel, this alternative would transition from a double-deck viaduct to two parallel structures. The alternative meets project design criteria and accommodates a main span cable-stayed, self-anchored suspension, or skyway design option. A bicycle/pedestrian path could be constructed as part of Replacement Alternative N-1. At the transition structure over YBI, the bridge would split from a double-deck structure to two parallel single-deck structures.

Replacement Alternative N-1 was defined, in part, to respond to recommendations from the MTC EDAP calling for an alternative that arched northward to maximize San Francisco skyline views for westbound bridge users and panoramic East Bay Hills and Oakland skyline views for eastbound users.

Replacement Alternative N-1 was defined as the northernmost alignment capable of providing skyline views while minimizing intrusion into Bay bottom geologic zones associated with the ancient Temescal Creek bed. This geologic zone contains deep mud layers. However, based on geologic data obtained after setting the alignment for Replacement Alternative N-1, it was determined that approximately one-half of it would fall within areas of deep Young Bay Mud, increasing the complexity, schedule, and cost of constructing the bridge substructure.

Although Replacement Alternative N-1 could be designed to maintain a lifeline vehicular connection in the event of an MCE, construction of the alternative would increase construction schedule and cost without providing substantially enhanced panoramic views when compared to other northern alternatives. Replacement Alternative N-1 was withdrawn from further consideration, and additional northern alternatives were analyzed for their ability to maximize user views while avoiding undesirable Bay bottom geologic zones.

2.7.2 Replacement Alternative N-3

This alternative, along with Replacement Alternatives N-4 and N-5, was defined through further refinements of northern alternatives. Studies were directed to meeting operational and safety design standards to the greatest extent possible, while placing the tower for the cable-stayed or self-anchored suspension design variations close to YBI, where geologic conditions are most favorable for the positioning of the tower footing that would, in turn, allow the main span to be positioned over the main navigation opening.

Replacement Alternative N-3 would place the main span tower approximately 110 meters (360 feet) offshore from YBI where distance to rock is approximately 20 meters (65 feet) with limited overlay of Young Bay Mud. Location of the tower at this site would facilitate construction schedule by reducing the amount of Bay excavation required.

Although tower placement would be optimized under Replacement Alternative N-3, the tower location would require the roadway horizontal and vertical alignments to be modified to less than optimum configurations, resulting in restricted sight distances which would affect driver response and, ultimately, roadway safety. The distance between the east YBI tunnel portal and the tower would require the westbound alignment to begin a northward curve immediately upon exiting the tunnel, resulting in restricted sight distance for westbound drivers approaching the tunnel portal. Roadway superelevation, the angle of tilt on a horizontal curve, would be limited to one percent. These design conditions would not meet American Association of State Highway and Transportation Officials (AASHTO) current design standards, requiring application for a mandatory design exception. A design exception would also be required because the westbound on-ramp from YBI would have inadequate sight distance. Replacement Alternative N-3 would also require using asphalt to build the height of the lanes on the upper deck of the YBI East Viaduct to connect to the new structure. Based on the inability of the Replacement Alternative N-3 to meet operational and safety design standards to the same extent as alternatives carried forward, it was withdrawn from further consideration.

2.7.3 Replacement Alternative N-4

Replacement Alternative N-4 was identified through refinement of northern alternatives. Replacement Alternative N-4 would place the main span tower 120 meters (394 feet) from YBI in the main navigation opening. The alignment would be south of Replacement Alternative N-1, minimizing intrusion into undesirable Bay bottom geologic zones.

Replacement Alternative N-4 was a modification of Replacement Alternative N-3 which provided for a 180-meter (591-foot) tangent (straight) roadway section at the YBI tunnel approach on the westbound alignment. This alternative was defined to prevent westbound traffic entering the tunnel portal on a curve. Replacement Alternative N-4 would meet the minimum roadway geometric operational and safety design standards. Overlay of the existing YBI East Viaduct upper deck roadway would be required to conform with the new westbound structure.

Although Replacement Alternative N-4 met minimal operational and safety design standards, geometric requirements would push the main span tower location further into the main navigation opening where distance to rock and depth of Young Bay Mud increased significantly compared to Replacement Alternative N-3. The increased depth to the main span tower would increase project cost and extend the construction schedule. Based on the deep water tower location, Replacement Alternative N-4 was withdrawn from further consideration, and alternative refinement studies were advanced.

2.7.4 Replacement Alternative N-5

Replacement Alternative N-5 represented a continuation of northern alternative refinement studies. Replacement Alternative N-5 would place the main span tower 158 meters (518 feet) offshore from YBI. Compared to the alignments for Replacement Alternatives N-3 and N-4, Replacement Alternative N-5 consisted of a 6,000-meter (19,685-foot) radius curve on the westbound alignment. As with Replacement Alternative N-3, the westbound alignment would enter the YBI tunnel portal on a curve, although the large curve radius would reduce or eliminate sight-distance concerns associated with Replacement Alternative N-3. Replacement Alternative N-5 would increase the rate of superelevation to two percent, which meets minimum design standards. Elevating the deck of the existing YBI East Viaduct would be required to conform to the new westbound structure.

Based on the desire to place a tangent roadway section at the westbound alignment approach to the YBI tunnel portal and the need to place and maintain the main span tower as close to YBI as possible, Replacement Alternative N-5 was withdrawn from consideration in favor of Replacement Alternative N-6.

2.7.5 Replacement Alternative S-1

Replacement Alternative S-1 was developed to minimize the length of the new bridge by providing a tangent directed toward the Oakland shore. As such, it would enter and exit the YBI East Viaduct similar to the existing alignment, eliminating the alignment curves that would provide panoramic vistas of the East Bay hills and the San Francisco skyline. The length of the bridge would be 3,525 meters (11,562 feet).

Replacement Alternative S-1 and other southern alternatives were proposed to reduce impacts to redevelopment concepts planned on YBI by the City and County of San Francisco (CCSF). Draft land use redevelopment scenarios would be affected by all replacement alternatives; however, southern replacement alternatives would use areas of YBI with more limited redevelopment potential for CCSF.

Replacement Alternative S-1 would align the replacement structure parallel and to the south of the existing East Span. This alternative would affect the East Bay Municipal Utility District (EBMUD) sewer outfall that is aligned south of the existing SFOBB. The outfall is approximately 85 meters (280 feet) south of the existing bridge at its eastern end and 219 meters (720 feet) to the south at its western end (see Figure 2-19 in Appendix A). The offshore portion of the pipeline is approximately 1,600 meters (1 mile) long. This 2.44-meter (8-foot) diameter outfall pipe disperses treated effluent from the EBMUD main wastewater treatment facility located immediately to the east of the project area. The outfall and a dechlorination facility located on the Oakland Touchdown area are critical elements to the operation of the EBMUD main wastewater treatment plant.

EBMUD reviewed proposed Replacement Alternative S-1 and expressed concern that the construction of the replacement bridge structures and the transverse crossing of the outfall in the Bay could cause both short- and long-term damage to the facility and increase complexity of maintenance activities. The outfall facility is 50 years old and construction activities, such as pile driving and dredging, may affect the structural integrity of the pipeline. The outfall would be at risk of damage or ruptures that could cause the release of secondarily treated effluent into the Bay. If this were to occur, EBMUD could be held in violation of its National Pollutant Discharge Elimination System (NPDES) Permit and could incur substantial monetary fines levied by the San Francisco Regional Water Quality Control Board (RWQCB). As a result, EBMUD determined that relocation of the outfall and dechlorination facility would be required to avoid potential conflicts or incidents.

In response to consultation with EBMUD, Replacement Alternative S-1 was revisited. By reducing the horizontal curve radius of the structures adjacent to YBI, Replacement Alternative S-1 was modified to more closely parallel the existing East Span at the approach to the Oakland Touchdown area. The revisited Replacement Alternative S-1 would eliminate a transverse, crossing in the Bay of the EBMUD outfall structure by setting the alignment between the existing East Span and the outfall pipe. Although no direct alignment conflict with the outfall structure would occur, concern remained for construction-period impacts to the outfall. The potential for damage to the outfall during construction could involve additional environmental permitting, thereby causing schedule delays, and during a seismic event, potential for damage to the outfall and bridge structures would be increased due to the proximity of them. Further investigation revealed that proposed replacement bridge construction methods would require dredging for barge access that could not be accomplished within the area between the existing bridge and the outfall structure.

Based on the potential conflicts with the EBMUD sewer outfall, Replacement Alternative S-1 and revisited Replacement Alternative S-1 were withdrawn from consideration in the DEIS in favor of a southern alternative that minimized potential conflict with the outfall structure.

The City and County of San Francisco Modified S-1 Alternative

In a comment letter on the DEIS (see the City and County of San Francisco Planning Department letter dated November 23, 1998 in Volume II of this FEIS), the CCSF presented a southern alternative (referred to in this FEIS as the CCSF Modified S-1 Alternative). Under this alternative, the new bridge would be located south of the existing structure and designed to minimize bridge length between YBI and Oakland (like the previously withdrawn Replacement Alternative S-1). The CCSF Modified S-1 Alternative would consist of two parallel structures similar to those proposed for the replacement alternatives. This 3,450-meter (11,320-foot) long structure would provide a straight connection from YBI to Oakland, moving away from the TI/YBI developable land to the north with a single curve for each roadway at YBI.

The columns supporting the eastbound roadway where it crosses the EBMUD outfall pipe would straddle the structure with outrigger "frame" supports and provide an opening through the foundation pilings for the outfall pipe.

Further Study of Relocating or Straddling the Outfall

Since publication of the DEIS, relocation and straddling options for the outfall were further evaluated to determine the feasibility of the CCSF Modified S-1 Alternative. Because this alternative was withdrawn from consideration prior to the circulation of the DEIS, a supplemental DEIS was not warranted for this additional analysis. At the request of FHWA and the Navy, ACOE examined the feasibility of the CCSF Modified S-1 Alternative. ACOE reviewed reports, backup data, and analyses provided by Caltrans, CCSF, consultants, and EBMUD to provide an independent assessment of the risks, costs, complications, and schedule issues associated with constructing the bridge along the CCSF Modified S-1 Alternative alignment. In January 2000, ACOE compiled the results of its review in a report entitled "Assessment of the San Francisco-Oakland Bay Bridge Seismic Replacement Project’s Impact on the EBMUD Sewer Outfall."

Options. In addition to an option where bridge foundations are designed to straddle the outfall pipe, three outfall relocation options were examined: trench relocation, use of a tunnel, and partial relocation.

The trench relocation option would relocate the entire sewer outfall to the north with a crossover pipe connected to the onshore pipeline. For the pipe to be founded in dense sands, the bottom of the offshore pipe would have to be located at approximately 20 meters (66 feet) below MSL. In areas where the sand layer is deeper, sub-excavation of the soft sediments would have to be done to as deep as 25 meters (82 feet) below MSL and backfilled.

A tunnel option would also relocate the entire outfall to the north of its current position. This option was evaluated because relocating the outfall to the north of the alignment reduced the potential for damage to the outfall during construction or a seismic event. As a result, there were fewer issues to address in the environmental documentation and permitting processes, which would prevent schedule delays. In addition, the tunnel option could increase the design life of the outfall to over 100 years because the tunnel would be located within the stiff clay/dense sand layer below Young Bay Mud at approximately 30 meters (98 feet) below MSL. This location would also reduce the potential for damage to the bridge resulting from a shift of the outfall during a seismic event.

The partial relocation option, which was developed to minimize impacts from Replacement Alternative S-4, includes relocating a portion of the onshore pipeline. Under this option, the alignment would avoid the offshore portion of the pipeline, but would cross over the onshore portion of the pipeline just east of the dechlorination facility. This crossing may create the possibility for damage to the outfall during construction activities. The dechlorination facility would not be displaced. The CCSF Modified S-1 Alternative would cause the entire offshore sewer pipeline to be relocated to avoid major impacts to the design and construction of the bridge. The partial relocation option would not be applicable to the CCSF Modified S-1 Alternative because it would result in the relocation of the entire offshore portion of the outfall.

Costs. Straddling the outfall would require significant modifications to the structural and foundation design of the new bridge, special and costly pipeline protective measures, and innovative foundation installation. Due to numerous uncertainties in regard to these issues, the cost of the straddling option is difficult to estimate without conducting a detailed design study.

Based solely on existing estimates of construction costs, the tunnel option would cost $87 million, the trench relocation option would cost $72 million, and the partial relocation option would cost $17 million. In addition to the construction costs, other incremental costs range from $43 to $77 million and are identified below.

It is estimated that additional study costs would range from $1.8 to $3.8 million and include land and marine outfall surveys, geotechnical studies of outfall foundation, bedding material, and surrounding geology, seismic analysis to model interaction between outfall and the new bridge foundation, and condition assessment for the outfall before and after construction. Additional design and construction costs are estimated to range from $19.0 to $36.5 million. Secondary construction costs (e.g., cost of implementing a monitoring program, demolishing the Key Pier Substation, and relocating the maintenance access road) range from $17.1 to $28.2 million. Post-construction costs range from $5.5 to $8.3 million and include a post-construction condition assessment of the outfall and future operations and maintenance costs. The ACOE, at the conclusion of the independent review of the outfall crossing report, stated that construction costs would likely constitute nearly half of the incremental costs, but it is difficult to verify the magnitude of these costs because the highest itemized cost estimate reflects restrictions related to seasonal breeding and migration of wildlife that may not materialize. The ACOE, in summarizing its independent review, stated that a more defensible overall estimate was $35 to $70 million. Costs for possible outfall damage range from $14.5 to $24 million and include increased risk associated with handling and placement of piles, construction and columns of superstructure, construction of trestles, and access dredging.

These incremental costs do not include possible costs arising from daily fines for any National Pollutant Discharge Elimination System (NPDES) permit violations.

Advantages/Disadvantages. The straddling option would involve several construction challenges and future access to the outfall for maintenance and repairs would be more difficult due to the close proximity of new bridge columns and abutments.

Each of the outfall relocation options has distinct advantages and disadvantages when compared to the others.

Costs would strongly favor the partial relocation option, but this could only be implemented with Replacement Alternative S-4.

The trench relocation option’s advantages are a new offshore pipeline and a location for the outfall that would be clear of SFOBB southern alternatives. This is EBMUD’s preferred option. The disadvantages are higher costs, greater disruption to sensitive San Francisco Bay waters, and delays in project schedule of 3-5 years. These delays, which would also apply to the tunnel option, would result from preparation of a design, completion of the environmental review process, acquiring permits as necessary from BCDC, ACOE, National Marine Fisheries Service (NMFS), California Department of Fish and Game (CDFG), U.S. Fish and Wildlife Service (USFWS), and RWQCB, building the new outfall, and removing the existing outfall.

The tunnel option advantages are also a new offshore pipeline, a design life that is at least twice as long as the trench relocation option due to greater protection of the pipeline from seismic events and offshore hazards, fewer impacts to the Bay environment, and fewer schedule extensions due to reduced permitting. The disadvantages are higher costs, restricted access for maintenance of the pipe, and the delays of 3-5 years mentioned above.

Further schedule delays for all relocation options are likely to occur as a result of the negotiation process with EBMUD, which has requested indemnification in perpetuity. It is difficult to quantify how long negotiations would take. Also, if the integrity of the outfall becomes compromised during construction, it is likely that there may be construction delays while response measures are developed and implemented. Actual damage to the outfall leading to a violation of the NPDES permit may result in a shutdown of the entire bridge construction project while repairs take place.

The environmental review process mentioned above would involve production of a supplemental Environmental Impact Statement (SEIS) for all options to assess the likelihood of damage to the outfall during or after construction. The SEIS would be used to develop the appropriate response measures for potential sewage spills caused by outfall blockage and a resulting treatment plant failure.

Other Issues Related to a S-1 Alternative

In addition to the impacts to the EBMUD outfall, there are several other issues associated with the CCSF Modified S-1 Alternative.

Section 4(f) Use. The Oakland Army Base Reuse Authority (OBRA) Reuse Plan has designated 5.9 hectares (14.7 acres) at the westernmost portion of the former Army Base on the Oakland Touchdown as the site of a proposed public access shoreline park. The proposed Gateway Park has received the support of interested local, regional, state, and federal agencies. The EBRPD has taken the responsibility for being the lead agency to further plan and manage the park. The Gateway Park is a Section 4(f) resource pursuant to the Transportation Act of 1966 and, as such, receives protections from use by transportation projects.

The CCSF Modified S-1 Alternative would bisect the parcel of designated parkland and would reduce the size of the proposed park by approximately one-half. This alternative would use much of the westernmost end of the park property, where views of the Bay to the south and west are the most dramatic and where the presence of a park would most effectively enhance the experience of landfall for bridge users and for park visitors. The bridge structure would also be immediately adjacent to the remaining parkland, thereby increasing expected noise levels in the park. A southern alternative would result in a Section 4(f) use of the proposed park.

Besides using a Section 4(f) protected parkland, the CCSF Modified S-1 Alternative would cross directly above the historic Key Pier Substation, which is also protected by the provisions of Section 4(f). The alignment would either span the building or would require its dismantling. Dismantling would constitute a Section 4(f) use.

Main Span Tower Construction Complexity. Founding the main span tower in bedrock would be more cost and time efficient than founding it in Young Bay Mud. The tower for all southern alternatives would have to be constructed approximately 67 to 71 meters (220 to 233 feet) below the mudline to be founded on bedrock. As a comparison, under Replacement Alternative N-6, the distance to the bedrock ridge is 6 to 9 meters (20 to 30 feet) below the mudline, and under Replacement Alternative N-2, the distance to bedrock is 11 to 14 meters (36 to 46 feet) below the mudline. Underwater construction increases in difficulty and cost with greater water depth. Safety requirements are also substantially increased, which could affect project schedule and cost. Depending on maximum construction depths, specialized equipment may be needed.

Visual/Aesthetics. Aesthetically, a northern alternative provides for a greater range of views for bridge users. Southern alternatives do not provide panoramic vistas of the East Bay hills and the San Francisco skyline to the extent that the northern alternatives do.

Conclusion

Replacement Alternative S-1, revisited Replacement Alternative S-1, and the CCSF Modified S-1 Alternative were withdrawn from consideration because construction of other southern alternatives that do not conflict with the EBMUD outfall are less likely to cause schedule delays (an estimated 8-15 months minimum), cost increases in the millions of dollars, increased risk of environmental damage resulting from effluent release, and complexity of long-term maintenance.

2.7.6 Replacement Alternative S-2

Replacement Alternative S-2 represents a continuation of southern alternative studies. Replacement Alternative S-2 provided broader radius curves at the YBI transition areas, avoiding the need for design exceptions. In response to geometric constraints, the distance to rock suitable for tower footings would also be in excess of 61 meters (200 feet) below the mudline.

Construction staging to maintain five lanes of traffic in each direction would require construction of temporary detours eastward to the cantilever section of the existing East Span. Further investigation indicated that tie-in of the temporary detours to the cantilever section would be complex and could potentially compromise the structural integrity of the existing structure.

Replacement Alternative S-2 would avoid a transverse crossing of the EBMUD sewer outfall in the Bay.

Although Replacement Alternative S-2 would meet mandatory design standards at YBI and would avoid impacts to the EBMUD sewer outfall, it was withdrawn from further consideration due to concerns for the structural integrity of the existing cantilever section raised by connection of temporary detours.

2.7.7 Replacement Alternative S-3

Replacement Alternative S-3 represents a southern alignment design refinement to better address operational and safety geometric design standards in the YBI transition area. Replacement Alternative S-3 was set at the YBI approach to eliminate the need for design exceptions for superelevation of roadway curves. However, meeting geometric standards would move the main span tower away from YBI to a location where distance to rock suitable for tower footings would be in excess of 61 meters (200 feet). As explained under the CCSF Modified S-1 Alternative, the difficulty, cost, and safety of underwater construction increases with water depth. Specialized equipment may be required. And similar to Replacement Alternative S-1, Replacement Alternative S-3 would not provide bridge users with panoramic views.

Replacement Alternative S-3 would require construction of temporary detours similar to those described for Replacement Alternative S-2. This raised concerns for the structural integrity of the existing East Span cantilever span during construction.

Replacement Alternative S-3 would have impacts to the EBMUD outfall structure similar to those described for Replacement Alternative S-1.

Based on the inability to meet mandatory design standards for superelevation, constructibility issues for tie-in of temporary detours to the existing East Span, and impacts to the EBMUD sewer outfall, the Replacement Alternative S-3 was withdrawn from further consideration.

2.7.8 Double-deck Alternative

A double-deck replacement bridge was considered early in the evaluation of replacement alternatives. The double-deck alternative could be constructed on either northern or southern alignments. It would provide five vehicular traffic lanes in each direction and inside and outside shoulders.

Preliminary cost estimates, prepared by Caltrans in 1996, indicated the double-deck replacement alternative would be more expensive than the single-deck alternatives.

A double-deck structure would limit views for lower-level bridge users. Lower deck views would be restricted by the upper deck roadway and supports as they are on the existing bridge.

Concerns for seismic reliability of double-deck structures have been raised because of extensive damage suffered by existing double-decked structures in recent seismic events, particularly Loma Prieta earthquake damage to the existing overhead truss section of the Bay Bridge East Span. It was determined that a seismically reliable double-deck replacement alternative could be designed. One method would be to construct an upper deck supported by columns straddling an independently supported lower structure. The resulting bridge substructure would be similar in mass to columns and footings for parallel structures.

Based on concerns over interaction of two structures in such close proximity during seismic events and the inability of the double-deck structure to provide panoramic views, the double-deck replacement alternative was withdrawn from further consideration.

2.7.9 Design Variations Considered

Profile

Replacement alternative refinement studies evaluated options for the bridge profile, which is the rise in roadway elevation from the Oakland Touchdown area to the YBI East Viaduct connection. Three profile variations—level approach grade, constant grade, and elevated grade—were evaluated.

Level Approach Grade profile refers to a vertical alignment that would remain level and near the water surface from the Oakland Touchdown area and begin elevation rise as far west as possible to provide required navigation clearance of 41 meters (135 feet) and conform to the existing YBI East Viaduct. A main span cable-supported design variation would be on such a grade.

Constant Grade indicates a vertical alignment rising at a consistent grade from the Oakland Touchdown area to meet main navigation opening clearance requirements and conform at YBI. A main span cable-supported design variation would be on a constant grade. The skyway of a cable-supported design variation would be on a constant grade until leveling on the main span where the cable-supported portion of the bridge adjoins the skyway portion of the bridge.

Elevated grade modifies the constant grade design variation rise at a slightly elevated grade between the Oakland Touchdown area and the main span. A main span cable-supported design variation would be level.

Traffic operational characteristics of each profile variation were evaluated with emphasis on the effect of roadway grade on truck speeds climbing the westbound grade. The analysis concluded that the range of a truck climbing speed difference among the three design variations was approximately six seconds and was not a substantial differentiation among the options.

Because no operational benefits would result from any of the profile design variations, it was not necessary to carry profile design variations to further levels of design refinement. The aesthetic impacts of profile variations were evaluated because the profile defines the line that the structures would draw across the horizon. Minor differences in the three design variations would be perceived from most views. At EDAP public meetings, a general preference was stated for the elevated grade profile design variation, because cable-supported main span design variations would have a symmetrical appearance from distant views and would contribute to bridge users’ experience of passing through a portal.

There was no support for the level approach grade because it would have the appearance of the San Mateo Bridge, which, although functional and cost-effective, is considered to be inappropriate for the character sought for the East Span replacement structure. It was withdrawn from further consideration. Caltrans performed a value analysis that resulted in substantial cost savings by lowering the profile at the main span tower to a position that was similar to the constant grade variation and acceptable to the overall bridge architecture. Additionally, with the inclusion of a bicycle/pedestrian path constructed at the same grade as the bridge, the constant grade rather than the elevated grade would produce slightly slower downhill speeds for bicyclists and result in improved safety. The elevated profile was considered but withdrawn for structural, economic, and marginally improved bicycle/pedestrian safety reasons.

Main Span Tower Design Variations

Cable-supported main span design variations were refined under the guidance of the EDAP. Progress designs up to the 30-percent design level for a representative replacement (Replacement Alternative N-6) were developed by two independent teams of structural engineers and architects. Extensive public participation and feedback were sought as part of the EDAP review of cable-supported design variations.

Designs for main span towers presented to the EDAP included a single tower between the parallel roadways and two "portal" towers with interconnected parallel towers arching over each structure. Portal towers considered included "H"-shaped and arched towers through which suspended roadway structures would pass. Single- and dual-tower design variations were created for both the cable-stayed and self-anchored suspension design variations.

Single- and dual-tower configurations would meet seismic design criteria to provide a lifeline vehicular connection on the East Span alignment. Dual-tower configurations would require more columns and larger pile caps and footings compared to single-tower designs, increasing the amount of fill in U.S. waters and volume of Bay mud to be excavated during construction.

Following evaluation of seismic safety and aesthetic considerations, the EDAP recommended that main span design variations be designed with a single supporting tower. Based on the EDAP recommendation developed with extensive public comment during public meetings held in the spring and summer of 1998, the increased impacts to Waters of the U.S. required to construct dual towers, and the ability for all replacement alternatives to accommodate the single-tower main span design variations, the dual-tower design variation was withdrawn from further consideration.

Steel Retrofit

The option to retrofit the existing East Span columns with steel instead of encasing them in concrete was considered but was withdrawn from consideration.

The existing East Span has eccentrically braced steel frame towers that are the primary yielding (movement) points for seismic events. For the Retrofit Existing Structure Alternative, the primary yielding point for seismic events would be the junction of the substructure and the superstructure where the isolation bearings would be installed. Fundamental to this isolation strategy is that there would be no instability below the point of isolation. This would require that the existing towers be strengthened and stiffened. Concrete would provide this requisite stiffness.

It would also be possible to achieve the requisite stiffness using steel frames on the towers, but the construction methods are much more labor-intensive and costly than using cast-in-place concrete.

Other factors considered in selecting concrete encasement were that retrofitting with steel on a structure containing lead-based paint would require special measures for the protection of the public, workers, and the environment, and steel towers would require significantly more maintenance over the life span of the bridge.

Bicycle/Pedestrian Design Variations

Consideration of bicycle/pedestrian access options on East Span Project replacement alternatives was accomplished through a cooperative process among Caltrans, MTC, and members of the Bay Bridge Bicycle/Pedestrian Advisory Committee (BPAC). Alternative configurations for a path on the East Span replacement alternatives were considered in a series of workshops hosted by Caltrans in fall 1997 and early 1998. Several path locations were considered, including at-deck, below-deck, and above-deck, on either or both the westbound and eastbound structures; also considered was a path down the center between the decks. The outcome of the workshops, and

participation by the BPAC in the MTC Task Force public meetings, was the development of recommendations for either:

BPAC’s initial recommendation was a dual-path design, but was not selected by MTC because (1) the path on the north side of the westbound span heading uphill from Oakland to YBI could interfere with motorists’ views, and (2) for security purposes (on days when the number of path users is moderate, it would be better to have users on one path than spreading them over two paths). The cost of the two paths would be greater and would require construction of a connection to the Oakland Touchdown area on the north side of the westbound lanes. This area would be immediately bordered by sand flats, eelgrass beds, and Bay waters, which would involve environmental and construction access constraints that do not exist with the single-path design. Based on the MTC Task Force recommendation, the dual-path and no-path design variations were withdrawn from further consideration and the replacement alternatives’ descriptions were modified to include the single, south-side path.

2.7.10 Temporary Detours on Yerba Buena Island Considered and Withdrawn

Optional configurations and locations of YBI temporary detours were evaluated in an effort to avoid or minimize impacts to USCG and Navy facilities. Possible temporary detour configurations were to locate:

Each of these configurations was analyzed for construction feasibility, impacts to YBI resources, traffic operational impacts, costs, and impacts on the project schedule. Based on analysis of conceptual engineering designs for the temporary detour options, the temporary detour options described below were withdrawn from further consideration.

Replacement Alternatives N-2 and N-6 North-north Temporary Detour Option

The north-north temporary detour would start as a double-deck roadway that becomes two side-by-side roadways approximately 200 meters (1,312 feet) east of the YBI tunnel. The temporary detour would provide roadway connections from the eastern portal of YBI to the new eastbound and westbound main span structures and would not require connection to the existing truss bridge to accommodate traffic during construction. During construction, westbound traffic would travel directly from the new bridge to the westbound temporary detour lanes to the existing viaduct and tunnel, and eastbound traffic would travel directly from the tunnel and existing viaduct to the temporary detour lanes and onto the new bridge (see Figures 2-16.1 and 2-17.1 in Appendix A). The westbound lanes of the temporary detour would span the Admiral Nimitz house (Quarters 1), which was listed on the National Register of Historic Places in 1991. Quarters 1 is located within the Senior Officers’ Quarters Historic District, which is eligible for listing on the National Register of Historic Places.

To provide the necessary support for the westbound temporary detour, a column would need to be placed within the eastbound traffic lanes at the point where the temporary detour makes a transition from a double-deck roadway to a side-by-side roadway. This would include a separation of lanes to both sides of the column, with three lanes on one side and two on the other side.

It was determined that splitting the eastbound mainline traffic would not be acceptable, primarily for traffic safety reasons. The column, even with appropriate crash cushion protection, would present a hazard. A single incident at the location could directly affect the operations of all five lanes, resulting in significant traffic and safety issues. The eastbound on-ramp from YBI is also in close proximity to the location of this lane split and column, creating an additional friction point within that section of roadway. Placement of a critical structural support element in the middle of mainline traffic was therefore determined to be too high a risk with regard to driver safety and structural integrity. For these reasons, the north-north temporary detour was determined to be unacceptable for the northern alternatives.

Replacement Alternatives N-2 and N-6 South-south Temporary Detour Option

The south-south temporary detour would be a full-length double-deck structure located south of the existing transition structure. Westbound traffic would travel on the upper deck of the existing bridge to the upper deck of the temporary detour, then to the YBI viaduct and tunnel. Eastbound traffic would exit the tunnel onto the lower deck of the temporary detour, then onto the lower deck of the existing bridge.

Eastbound traffic traveling from the YBI tunnel would be split around several columns with three travel lanes on one side of the columns and two lanes on the other. This would create a hazardous obstruction in the middle of mainline traffic lanes similar to that for the north-north temporary detour.

The south-south temporary detour option would minimize temporary ground disturbance to U.S. Navy property on YBI, although temporary impacts to the USCG station would increase. Construction of the south-south temporary detour options would require that an 88-meter (288-foot) section of the existing bridge be cut away and removed and replaced with the temporary detour. The replacement section would be constructed on YBI, then lifted in place. This replacement operation would require complete closure of the existing East Span in both directions for a period lasting days. The total number of consecutive days of bridge closure is not known, but is estimated to be two weeks minimum. Because of the magnitude of the task to detach and remove the section of the existing bridge, potential for the construction period to be extended would be great.

Based on the hazards to motorists caused by complexity of construction and the requirement for complete closure of the entire East Span over a number of days, the south-south temporary detour option was withdrawn from further consideration.

Replacement Alternative S-4 North-north Temporary Detour Option

The north-north temporary detour option for Replacement Alternative S-4 would be a double-deck structure constructed north of the existing transition structure and existing East Span. Westbound traffic would travel on the upper deck of the existing bridge to the upper deck of the temporary detour then to the YBI tunnel. Eastbound traffic would exit the tunnel onto the lower deck of the temporary detour, then onto the lower deck of the existing bridge.

The north-north temporary detour option would be constructed as described for the south-south temporary detour option. It was withdrawn from further consideration for the constructibility and traffic operations reasons discussed for the south-south temporary detours.

Replacement Alternative S-4 South-south Temporary Detour Option

A south-south temporary detour for Replacement Alternative S-4 would be two parallel structures. Westbound traffic would be temporarily detoured from the existing bridge to the new structure and back to the tunnel. The eastbound structure would be placed south of the transition structure and existing East Span.

A south-south temporary detour option was identified for its potential to avoid temporary disturbance to U.S. Navy properties. However, it would have placed a temporary detour over residential buildings at the USCG station and temporary detours in the Bay. More detailed investigation indicated that the south-south temporary detour option would affect construction staging for Replacement Alternative S-4. Construction of the westbound temporary detour would conflict with placement of columns for the replacement structure and construction of the eastbound deck of the replacement structure. Based on the construction phasing conflicts, the south-south temporary detour option was withdrawn from further consideration.