The Sir Francis Drake Boulevard bridge is located in the community of Point Reyes Station, just west of State Route 1, in Marin County and immediately south of the confluence of Olema Creek with Lagunitas Creek. The proposed project will replace the existing bridge over Olema Creek with a new structure which will accommodate two 12-foot-wide travel lanes (one lane in each direction) with 8-foot-wide shoulders, resulting in a bridge width of approximately 44 feet (includes bridge railings).
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 current Sir Francis Drake Boulevard bridge is a two-lane, major collector that serves two-way traffic with a posted speed limit of 45 miles per hour. The roadway currently includes 11-foot lanes with one-foot shoulders in each direction.
The new bridge will be a cast-in-place, post-tensioned concrete slab unit supported over driven steel pipe piles. The project site is adjacent to the San Andreas Fault and the new bridge will be designed to withstand forces expected to occur during an earthquake.
Construction is expected to take one 6-month long construction season. Construction activities within the banks of Olema Creek would be performed between June 15 and October 15, which would correspond to when there is little or no precipitation and when stream flow is lowest. Work within the Olema Creek channel would be necessary in order to install temporary shoring, remove the existing piers and abutments, install new abutments, and place rock slope protection. A temporary creek diversion is proposed to dewater the work area within the creek bed during the construction window.
Project construction would remain primarily within the County’s right-of-way; one right-of-way acquisition would be required on the south side of Sir Francis Drake Boulevard from the National Park Service (APN 166-170-03) for roadway repaving. Temporary construction easements would be required from several parcels in order to provide access to the creek, allow for storage and staging areas, and other project necessities.
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 $3 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 the existing bridge is removed and while the new bridge is constructed, Sir Francis Drake Boulevard will be closed at the project location and a 4.1-mile detour along the Bear Valley Road will be utilized. The detour would add approximately seven minutes of travel time for motorists. View detour map.
Marin County Public Works will engage in public outreach with the community as the project construction date draws nearer.
- Jason Wong, Senior Civil Engineer: 415-473-6192
- Construction TBD