Nicasio Valley Road Bridge Replacement



The proposed Project will replace the existing bridge over Nicasio Creek, located approximately 200 feet south of the intersection of Nicasio Valley Road and Lucas Valley Road, with a new structure accommodating two 11-foot-wide lanes with 5-foot-wide shoulders and bridge barriers, resulting in a bridge width of approximately 36 feet. The new structure will be a 110-foot-long, single-span, precast, prestressed concrete California wide-flange girder bridge. The alignment of Nicasio Valley Road will shift to the east by approximately 13 feet to allow for stage construction of the new bridge.

Bridge demolition and construction will occur in two stages over two construction seasons between June 15 and October 15. In both stages, a creek diversion will prevent any demolition and construction work from occurring within the flowing creek channel. Stage one will consist of construction of the eastern span of the new bridge in a new alignment, 13 feet east, and the subsequent demolition of the existing eastern bridge span and related substructure. Stage two of bridge construction and demolition will focus on the western span of the bridge. The abutments, foundations, and cast-in-place bridge deck for stage two will be constructed in the same manner as in stage one.

As is standard with all Marin County Public Works projects, the contractor will be required to control any runoff or erosion from the project site into any/all nearby waterways and conduct a full site cleanup once project is complete.


The estimate for the project is $4.5 million dollars. The project is federally funded by a grant from the Highway Bridge Program (HPB).  The purpose of the HPB is to replace or rehabilitate public highway bridges over waterways or other topographical barriers including highways or railroads.

Traffic Impacts

Nicasio Valley Road and Lucas Valley Road are expected to remain open to traffic throughout construction. Stage construction will be implemented to maintain traffic operations during construction. For the first stage of construction, two-way traffic will remain on the existing bridge, while part of the replacement bridge is constructed and portions of Nicasio and Lucas Valley roads are widened. The first stage is expected to take approximately six months. The second stage will consist of one-way traffic control along the newly constructed bridge (stage one), with signals along Lucas Valley Road, Nicasio Valley Road, and the private driveway controlling access. The second stage is expected to take approximately six months.  Access to all private driveways will remain throughout construction.



  • Q2/Q3 2024 – Secure NEPA clearance
  • Q3/Q4 2024 – Start environmental permitting, utility coordination, and temporary construction easements
  • Construction TBD
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