The proposed project will replace the existing bridge over San Geronimo Creek with a new structure accommodating one 12-foot-wide lane with 2-foot-wide shoulders and bridge railings, resulting in a bridge width of approximately 20 feet. The bridge location is on Mountain View Road just off Sir Francis Drake Boulevard in the community of Lagunitas-Forest Knolls in unincorporated Marin County.
The project includes removal of the existing bridge, which has been deemed functionally obsolete by Caltrans (who inspects all bridges in Marin) and ready for replacement. The project will also include construction of retaining walls along the top of the south creek bank. The new bridge will be a 70-foot-long, single-span, precast, prestressed concrete slab unit. The roadway profile of the bridge will be raised approximately 4 feet to clear the 100-year flood water elevation, as its current configuration has a history of flooding.
To account for the bridge’s new 4-foot height increase, the roadway profiles of the approaches on Sir Francis Drake Boulevard (Mountain View Road and Corona Avenue) will be raised and repaved. This work will involve the removal of existing pavement and the placement of new pavement.
On the north side, the roadway approach work will start at the Mountain View Road and Sir Francis Drake Boulevard intersection, raising the center of the intersection by 2 feet. The roadway approach work will extend 440 feet along Sir Francis Drake Boulevard (238 feet to the west and 202 feet to the east), gradually conforming to the existing roadway.
The southern roadway approach work will start at the Mountain View Road and Corona Avenue east intersection, raising the center of the intersection by 4 feet. The roadway approach work will extend 60 feet down Corona Avenue east, 25 feet down Corona Avenue south, 95 feet down Mountain View Road, and gradually conforming to the existing roadways.
Temporary construction easements will be required from several parcels to allow for the reconstruction of driveways, enable access to the creek, and provide adequate storage and staging areas. Construction activities within the banks of San Geronimo Creek will be performed between June 15 and October 15, which corresponds to when there is little to no precipitation and when stream flow is at its lowest.
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 (i.e. San Geronimo Creek) and conduct a full site cleanup once project is complete.
The estimate for the project is $4.1 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.
After existing bridge is removed, access to Corona Avenue will be via a 1.1 mile detour across the Lagunitas Road bridge. The proposed design will utilize precast concrete elements for the new bridge, which will expedite construction. The County will engage in public outreach with the community as the project construction date draws nearer and detour/access plans are solidified.
- Friday, November 4, 2022 – Project presentation at Lagunitas Technical Advisory Committee Meeting
- TBA 2023 – Local neighborhood meeting
- 2023 – Environmental permitting process
- Spring 2024 – Expected start of construction
- Fall 2024 – Expected completion of construction