Sir Francis Drake Boulevard Bridge Replacement Project

The Marin County Department of Public Works is proposing to replace the existing bridge over Olema Creek along Sir Francis Drake Boulevard. The existing Sir Francis Drake Boulevard (Blvd) is a two-lane, 24-foot wide, major roadway that serves two-way traffic with a posted speed limit of 45 miles per hour. The roadway currently includes 11-foot lanes with 1-foot shoulders in each direction. The existing bridge was originally constructed in 1930, lengthened in 1967, and was recently rated as being functionally obsolete, meaning the bridge fails to meet current functional standards. Additionally, based on a preliminary hydraulic analysis, the existing bridge is not high enough to clear the 100-year storm event, nor does it clear the 50-year storm event with two feet of freeboard, a safety factor used to express feet above flood level for purposes of floodplain management. 

Bridge replacement will include replacing the existing bridge structure with a new structure that is wider, longer, and higher. Construction of the bridge will involve excavation for, and construction of, concrete abutments supported on driven piles. Construction of the roadway approaches will involve the removal of existing pavement and the placement of fill material, aggregate base, and hot mix asphalt pavement. Tree removal and the removal of other vegetation along the creek banks will be necessary for the Project. Temporary falsework to support the cast-in-place structure while it reaches full strength will be required within the dewatered waterway. Other temporary work within Olema Creek that is anticipated includes removal of the existing bridge, including existing abutments, piers, foundations, and wingwalls; installation of new abutments; and installation of scour countermeasures. A temporary creek diversion is anticipated in order to complete these activities within the waterway. Relocation of overhead and underground utilities is anticipated as part of the Project. Construction is expected to begin in spring 2028 and is anticipated to have a duration of six months.