Project Development

Due to the age and condition of the existing Bon Air Bridge, replacement is more economically feasible than continued periodic maintenance and repair. The project will replace the existing bridge with a new bridge that follows the same general alignment. One vehicle lane will be maintained in each direction and the new bridge will be widened to accommodate bike lanes and multi-use paths on both sides.

The new bridge will reduce the number of spans and columns to less than half of the number that currently exists, thereby improving the conveyance capacity of the creek.

Achievements to Date

The City applied for a grant to replace the bridge in 2002. A Highway Bridge Replacement and Rehabilitation grant was awarded for the project, and Caltrans authorized the preliminary engineering of a bridge replacement to begin in January 2002. Preliminary work started in 2006 with the filing for federal funding. Construction started in spring 2018 and is anticipated to last four years.

Seeking public input on the replacement project, the City presented various conceptual designs for a new bridge to the Larkspur City Council and the public during City Council meetings on June 4, 2008; August 20, 2008; and December 3, 2008. A public meeting was also held on the proposed replacement bridge on June 26, 2008.

conceptual_illustration

Conceptual bridge illustration presented to the public in 2008.

At the June 26, 2008 meeting, different conceptual designs were presented, including designs featuring suspended sidewalks, an arch and trapezoidal girder system, or lighted overlooks. The public provided feedback on these designs, including suggestions to:

  • Draw attention to and accentuate the natural landscape
  • Reflect the wide, flat stream at the point of crossing
  • Keep views of the surrounding hills open from the bridge
  • Connect the bridge seamlessly to the Corte Madera Creek Pathway
  • Include aesthetic treatments on the sides of the bridge
  • Include lights that are short and downward on the bridge to avoid light pollution and glare impacts for those living near the bridge

The City worked intensively to incorporate this feedback and selected a final design for the replacement bridge that reflects the extensive community outreach process, improves the safety of pedestrians and bicyclists with a protected multi-use path on both sides, and brings the bridge up to current seismic design and safety standards.

A motorist and bicyclist sharing the road on the existing bridge. The replacement bridge will have barrier-protected multi-use paths on both sides in addition to dedicated bike lanes.

A motorist and bicyclist sharing the road on the existing bridge. The replacement bridge will have barrier-protected multi-use paths on both sides in addition to dedicated Class II bike lanes.

Environmental Review, Permits and Utility Coordination

With the approval of the design direction for the bridge, the City moved forward with environmental review and securing regulatory agency permits for the project. In addition, the City coordinated with the various utility companies whose infrastructure was attached to the old bridge and would need to be accounted for in removing and replacing the bridge.The project completed environmental review (both state and federal) in 2012. Following environmental review, the City completed permits with the following regulatory agencies required for construction:

  • Army Corps of Engineers
  • United States Fish and Wildlife
  • California Department of Fish and Wildlife
  • Bay Conservation and Development Commission
  • Regional Water Quality Control Board

The permitting process triggered five mitigation projects that are to be completed before the end of the bridge construction. More information on the mitigation projects is available HERE.

Permitting was completed in 2015. Utility relocation started in 2015 with AT&T boring a new casing under Corte Madera Creek to accommodate the cables attached to the old bridge. A temporary overhead line was installed by PG&E and the Marin Municipal Water District made arrangements for a replacement water line to be hung under the new bridge.

The City advertised the project for construction bids in late 2016 but did not award a contract due to the low bid exceeding the engineers cost estimate and the Caltrans authorized funding. Contractor feedback was that the environmental constraints on the project, and the need to keep the bridge open during construction resulted in escalated costs. In mid-2017 the City Council weighed the option of allowing the bridge to be closed during construction to keep construction costs lower. This option was not acceptable the public, and Council directed staff to seek the additional funding from Caltrans and re-advertise the project with the bridge being kept open during construction.

Bids were opened in January of 2018 and Golden State Bridge Inc, (GSBI) from Benicia. CA was determined to be the low bidder. GSBI’s first work day on the project was May 23, 2018.