Design Review Process
The design for the new East Span has been developed with extensive input from public hearings, public comment on the environmental document, and coordination with the Metropolitan Transportation Commission (MTC). Two advisory committees were created by MTC specifically for this project: The Bay Bridge Design Task Force (BBDTF) and their technical advisory committee, the Engineering and Desing Advisory Panel (EDAP). The BBDTF has reviewed the East Span Project from the initial stages of choosing the bridge design materials and alignment through detailed development of elements such as lighting and a bicycle/pedestrian path.
For more information on the East Span design review process, visit the East Span Project newsletter archives.
The new East Span would consist of two side-by-side bridge decks, each with five lanes plus shoulders, and a bicycle/pedestrian path. In addition to addressing seismic concerns, the new bridge would provide critical operational and safety improvements over the current bridge, including shoulders and standard width lanes. The existing bridge would be dismantled.
Proposed Bridge Alignment
Several alignments were considered for the new East Span. Since the existing bridge must be operational while the new bridge is constructed, the new bridge must be built either north or south of the existing bridge. After extensive environmental review and geologic testing, Caltrans has identified northern alignment N6 as the Preferred Alternative for the new East Span.
The N6 alignment would avoid portions of the Bay where geologic conditions would increase construction complexity and cost. The N6 alignment would allow for easier access to bedrock to construct the main span tower. The alignment would also accommodate the East Bay Regional Park District's (EBRPD) planned Gateway Park on the Oakland shore and minimize conflicts with facilities and operations of the U.S. Coast Guard, the East Bay Municipal Utility District's sewer outfall, and the Port of Oakland's expansion plans. For more information about Caltrans' coordination with local agencies and project stakeholders, click here.
MTC's Recommended Design for New East Span
MTC and EDAP have also recommended the N6 alignment. EDAP concluded that this replacement alternative would create the best "gateway" to Oakland, while enhancing vistas, and allowing more flexibility to design and build a cable-supported span. The N6 replacement alternative would provide expanded views toward the Golden Gate, Mt. Tamalpais, and portions of the San Francisco skyline for westbound motorists. As with any of the alignments considered, eastbound motorists would have panoramic views of the Oakland skyline and the East Bay hills.
In June 1998, MTC recommended that Caltrans pursue a signature bridge design option which includes a steel single-tower suspension span over the shipping channel near Yerba Buena Island and a concrete pier-supported "skyway" from the suspension span to Oakland. MTC noted that the suspension span's single-tower and self-anchoring features represent important advances in bridge and seismic design and that the design would provide an appropriate and distinctive gateway to the East Bay. The catenary forms of the suspension span also relate to the context of the proposed bridge, mirroring the lines of the West Span of the Bay Bridge and the Golden Gate Bridge.
After considering several possible profiles to accommodate the grade change between the tunnel on Yerba Buena Island and the Oakland shore, MTC recommended an elevated profile for the new span. This means that the suspension span will remain at a relatively constant grade at approximately the level of the tunnel and the skyway will slope gradually down toward the Oakland shore. [The diagram shown here is vertically exaggerated for illustration purposes].
MTC recommended that the new span include a 15.5-foot wide bicycle/pedestrian path, built one foot above roadway level on the south side of the eastbound deck.
EDAP and the design team envision the bridge as a "white line" across the Bay. The new bridge rises from the Oakland shore toward the suspension span over the shipping channel and then connects to the existing tunnel on Yerba Buena Island. All vertical elements, including the tower, piers, and light standards have been designed with faceted forms to emphasize the clean modern lines of the structure and intensify the effects of light and shadow. Though the concrete portions of the bridge are not bright white, their pale gray color and clean linear character support the "white line" vision for the bridge. The bridge will carry eastbound and westbound traffic on separate, parallel road decks. The decks will converge into a double-deck configuration as they approach the Yerba Buena Island tunnel and the West Span of the Bay Bridge. The bicycle/pedestrian path terminates on the island.
From the Oakland shore to the suspension span, the bridge consists of a pier-supported concrete skyway. Designed for optimum seismic performance with consideration of the deep Bay mud in this area, the skyway will appear as a clean pale line accented by the faceted vertical forms of the pier and light standards. The roadway light standards increase in height as the bridge rises over the water and approaches the suspension span.
The asymmetrical suspension span has a longer forward
span (east of the tower) than back span
which provides a more gradual transition from
the gently sloping skyway and gives the East Span a distinctive silhouette.
The 530-foot tall steel tower is located between the two road decks
and is made up of four pentagonal columns connected by a series of horizontal
West of the suspension span, the two roadway decks decrease in thickness as they transition to a double deck structure in order to connect to the existing tunnel and West Span. The bicycle/pedestrian path descends along the eastbound on-ramp and terminates on the island.
The above design recommendations were also adopted by the San Francisco Bay Conservation and Development Commission (BCDC), a state agency dedicated to protecting and enhancing the Bay and ensuring that the surrounding development incorporates maximum feasible public access.
MTC continues to provide key input to the East Span Project to ensure that region-wide interests are appropriately addressed. A description of MTC's recent recommendations are listed below.
Recommendations Incorporated into the Design
MTC’s Bay Bridge Design Task Force recommended modifying the design of the bicycle/pedestrian path to include several belvederes or rest stops along its length. The belvederes will provide space for pedestrian and bicyclists to rest at various points along the span and enjoy sweeping views of the Bay and hills.
Additionally, the Task Force recommended using earth fill rather than structural elements to support the roadway at the Oakland touchdown. Earth fill will provide better seismic safety performance and will be easier to repair after a seismic event. This approach also enhances the appearance of the bridge touchdown by eliminating the concrete piles and adding a planting area.
The Task Force has also supported Caltrans’ proposal to install motion detectors on the East Span. These detectors measure a structure’s response to earthquakes. The data provided by the detectors on the new East Span is necessary to confirm acceptable seismic performance and will be useful in designing future structures.
Recommendations Not Currently Incorporated into the Design
MTC supports the concept of the bridge as a "white line" across the Bay." Originally, both the steel and concrete portions of the bridge were envisioned as white. MTC did not authorize the extra funding to pay for white concrete. However, MTC is still interested in discussing options for concrete coloring. At MTC’s Engineering and Design Advisory Panel meeting on December 7, 2000, the following suggestions were made: (a) the concrete on the exterior side girders of the viaduct should be as light and as consistent in color as possible; (b) the steel portions of the bridge should be painted to match the color of the concrete on the viaduct side girders.
MTC continues to support inclusion of a "light pipe" along the outside edges of the East Span to unify the appearance of the bridge and add to its distinctiveness with a white line of light. However, the light pipe is not an eligible amenity for which MTC can extend the seismic retrofit toll surcharge. MTC will seek funding for this design enhancement in the context of the expected legislative deliberations in 2001 on providing additional funding for the overall toll bridge seismic retrofit program. Caltrans is making provisions in the current design so that the light pipe can be added later if funding is identified.
Pending specific recommendations and funding for these elements, Caltrans is continuing the detailed bridge design process using "baseline" design features, which are focused on safety and economy.
Lighting A Bridge For the 21st Century
The East Span would usher in the 21st century and would serve as a bright new gateway connecting San Francisco, Oakland, and the East Bay. Caltrans’ design team has developed a lighting strategy that would appropriately showcase this important landmark. Caltrans' Project Manager Brian Maroney says that lighting for the East Span Project is intended to serve two purposes; safety and aesthetics.
Maroney explains that the proposed lighting strategy would provide appropriate visibility for night driving on a major roadway. Lighting on the entire East Span is aimed in the same direction as moving traffic to eliminate glare that can occur from ordinary roadway lights.
The roadway light standards are pentagonal in cross section, in keeping with the faceted architectural vocabulary of the tower and piers. As the bridge rises over the water from east to west, the pole heights increase in a progression toward the dramatically lit suspension span.
Two of the risk design's prominent features would be the main suspension tower and the cables that join the structure to the roadbed. The lighting strategy is intended to treat these elements in a way that best displays their architectural form and calls for the main tower to be illuminated with brightness increasing towards the top to emphasize the structure's soaring height. A marker light at the top of the tower would further accentuate the height while creating a dramatic end point.
Lights at the base of the tower would illuminate the underside of the suspension span, highlighting the structure and creating a reflected image in the water. Lights would also be placed inside the tower to clearly delineate the structure's open design. Additionally, the main cable and all suspender cables would be illuminated, revealing them clearly and showing how the span would be joined to the tower.
Lighting on both the skyway and the suspension span portions of the bridge was designed to provide Oakland and the East Bay with dramatic nighttime views.
A bridge is a true landmark. It joins two places and acts as an invitation to enter a community. Caltrans lighting designers are working to ensure that the bridge will be a significant landmark for the 21st century.