SR-84 West Union Creek Bridge Replacement

The West Union Creek Bridge Replacement Project (2W780) aims to modernize an important stretch of State Route 84 (SR-84) in San Mateo County. SR-84, also called Woodside Road, serves as a vital connection between inland communities and the coast. The existing bridge, originally built in 1903, is narrow, aging, and no longer meets today’s seismic or safety standards. In addition, the bridge’s low clearance restricts native fish from moving freely through the creek and creates conditions that do not adequately support healthy aquatic habitat.

To improve safety and mobility, the project proposes replacing the current bridge with a new structure that meets modern engineering requirements. The updated design will widen the roadway, strengthen resilience during earthquakes, and provide space for bicyclists and vehicles to travel more comfortably. The project also seeks to enhance how West Union Creek flows beneath the bridge, supporting healthier natural habitat conditions and reducing erosion and flooding risks.

Construction of the project would require a full closure of SR-84 at the bridge location due to the narrow existing structure and constrained work area. Traffic would be detoured along established routes, including SR-84, Whiskey Hill Road, Sand Hill Road, and Portola Road, for an approximate distance of 4.5 miles.

Planning and community engagement are key components of this effort. The project team is currently preparing environmental studies prior to the design phase of the project. Caltrans will hold public meetings to give residents and drivers an opportunity to comment on the project.

Schedule

The project is currently in the Environmental Phase of project development. This phase will be followed by the Design phase and then Construction. Listed below are target dates for completing the various phases of project development.

Environmental Documents (PAED) Complete: Spring 2027 (Target)
Design (PS&E) Complete: Spring 2029 (Target)
Begin Construction: Fall 2031 (Target)
End Construction: Fall 2033 (Target)

Construction dates may change due to weather.

Project Contact

Jeneane Crawford
Public Information Officer - Caltrans District 4
Jeneane.Crawford@dot.ca.gov
510-286-0319

 

Page updated July 2026