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Marin-Sonoma Narrows Home

Project Information

Alternatives
HOV Improvements
Expressway Upgrade

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Alternatives


As part of the environmental review for the project, Caltrans will evaluate alternatives for each project segment. For Segments A and C, there are only two alternatives: “Build” or “No Build”. (These segments are already built to freeway standards, so the needed improvements aren’t as extensive as in Segment B (Central Segment), which is currently built to expressway standards and needs much more work).
For Segment B (Central Segment), under the “Build” alternative, four freeway access alternatives are currently under consideration, subject to the review of several resource agencies and environmental review.



HOV IMPROVEMENTS

Segment A (Southern Segment) - Route 37 to Atherton Avenue in Novato (approximately 4 miles)

“No Build” Alternative:
No changes or upgrades to the existing roadway

“Build” Alternative:
Proposes to add contiguous HOV lanes to the existing six-lane freeway with all of the widening in the existing median. The addition of these lanes will also require that the following improvements be made:

  • Upgrade median drainages
  • Add concrete median barrier
  • HOV-bypass and ramp metering to all on-ramps
  • Add soundwalls and retaining walls
  • Widen Novato Creek Bridge
  • Widen Franklin Overhead Bridge
  • Widen Olive Uncrossing Bridge
  • Widen North Novato Overhead Bridge


    Segment C (Northern Segment) - Route 116 (East) to Old Redwood Highway in Petaluma (approx. 4 miles)

    “No Build”
    Alternative:
    No changes or upgrades to the existing roadway

    “Build” Alternative:
    Proposes to add contiguous HOV lanes to the existing six-lane freeway with all of the widening in the existing median. The addition of these lanes will also require that the following improvements be made:
  • Upgrade median drainages
  • Add concrete median barrier
  • HOV-bypass and ramp metering to all on-ramps
  • Add soundwalls and retaining walls
  • Replace Northbound 101/116 Separation and Overhead, widen Southbound
  • Widen Washington Creek Bridge
  • Widen Lynch Creek Bridge
  • Replace North Petaluma Overhead Bridge


    EXPRESSWAY UPGRADE

    Segment B (Central Segment) – “The Narrows” - Atherton Avenue to north of Route 116 (East) – Novato to Petaluma (approx. 9 miles)

    “No Build”
    Alternative:
    No changes or upgrades to the existing roadway

    “Build” Alternative:
    Proposes to upgrade the existing four-lane expressway to freeway, with the addition of continuous HOV lanes. The addition of these lanes, as well as the freeway upgrade, require that the following improvements be made:

  • Upgrade median drainages
  • Add concrete median barrier
  • Add various interchanges and frontage roads (see access alternatives below)
  • Replace bicycle facilities

    Although the median in certain portions of Segment B (Central Segment) is sufficient for mainline widening, this is not consistently the case; therefore, widening the roadway for HOV lanes would also require mainline realignment in certain portions, involving the following:
  • Replacing the cattle undercrossing at Dairy/San Antonio Road
  • Constructing a new San Antonio Creek freeway bridge
  • Removing the existing southbound San Antonio Creek freeway bridge
  • Removing the existing Petaluma Boulevard Undercrossing freeway bridges
  • Replacing Petaluma River Bridge

    Segment B (Central Segment) Freeway Access Alternatives
    In addition to roadway realignment, the proposed freeway upgrade in Segment B (Central Segment) would eliminate at-grade access to US 101. Therefore, one of these access alternative combinations would be selected, subject to review and consensus of resource agencies.

    Alternative 4B (see map)


  • Extend Redwood Boulevard north to Olompali Park.
  • Convert Redwood Landfill Overcrossing to a diamond interchange. New frontage roads would occur up to Redwood Landfill on the eastern side of US 101 and up to the Marina on the opposite side of the freeway, west of the railroad tracks and slough.
  • Construct a diamond interchange just south of San Antonio Road. Add new bridge at creek, just east of existing bridge. New frontage roads are proposed on the eastern side of US 101 up to Skinner Road using existing northbound San Antonio Creek Freeway Bridge.
  • Construct diamond interchange at Petaluma Boulevard South. New frontage roads would be southward on the western side of freeway up to Cloud Lane and southward on the eastern side up to Gambini Road.
  • Class I Bikeways would be located (1) along Olompali Park and along west side of freeway between Redwood Landfill and San Antonio Interchanges (2) along San Antonio Creek, and (3) along eastern side of freeway opposite Cloud Lane.

    Alternative 12B (see map)

  • Extend Redwood Boulevard north to Olompali Park
  • Convert Landfill Overcrossing to diamond interchange – new frontage road locations: (1) up to Redwood Landfill and Marina on west side of the railroad and slough (east), (2) up to San Antonio Road, upgrade San Antonio Road and add new bridge at creek (west).
  • Construct diamond interchange at Petaluma Boulevard South – new frontage road locations: (1) to Cloud Lane (west) and (2) across San Antonio Creek using existing northbound San Antonio Creek Freeway Bridge (east).
  • Class I Bikeways – Along Olompali Park, and San Antonio Creek.

    Alternative 14B (see map)

  • Extend Redwood Boulevard north to Olompali Park.
  • Construct diamond interchange just south of San Antonio Road – New frontage road along west side of freeway at daily (using existing overcrossing) to landfill and marina on west side of railroad and slough (east).
  • Upgrade San Antonio Road and add new bridge at creek (west), new frontage road location: (1) to Skinner Road (east) using existing northbound San Antonio Creek Freeway Bridge.
  • Construct diamond interchange at Petaluma Boulevard South – new frontage roads to Cloud Lane (west) and Gambini Road (east).
  • Class I Bikeways – Along Olompali Park, along San Antonio Creek and Along east side of freeway opposite Cloud Lane.

    Alternative 14D (see map)

  • Extend Redwood Boulevard north to Olompali Park
  • Construct diamond interchange just south of San Antonio Road – New frontage road locations: (1) along east side of freeway at Silveira Dairy up to Redwood Landfill and (2) along the Marina on the west side of the railroad tracks and slough (east). Upgrade San Antonio Road and add new bridge at creek (west), new frontage road to Skinner Road (east) using existing northbound San Antonio Creek Freeway Bridge.
  • Construct diamond interchange at Petaluma Boulevard South – New frontage roads: (1) to Cloud Lane (west) and (2) to Gambini Road (east).
    Class I Bikeways – Along Olompali Park, along San Antonio Creek, and along east side of freeway opposite Cloud Lane.

    How were the access alternatives chosen?
    The access alternatives were evaluated with a matrix approach, using input from the community at public scoping meetings and the Policy Advisory Group meetings.
    Download (1-2MB ) the Evaluation Criteria Matrix results and description here:

  • Coverage
  • Evaluation Criteria Matrix Summary
  • alternative1.pdf
  • alternative2.pdf
  • alternative3.pdf
  • alternative4.pdf
  • alternative5.pdf
  • alternative6.pdf
  • alternative7.pdf
  • alternative8.pdf
  • alternative9.pdf
  • alternative10.pdf
  • alternative11.pdf
  • alternative12.pdf
  • alternative13.pdf
  • alternative14.pdf
  • alternative15.pdf

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