Monte Rio Bridge Retrofit

The project would strengthen the existing Bohemian Highway Bridge over the Russian River to reduce the risk of collapse during a major earthquake. Rather than constructing a new bridge, the project would retrofit the existing bridge with new structural supports and connections.

The bridge was constructed in 1934 and does not meet current seismic design standards. Engineering analysis identified vulnerabilities that could increase the risk of collapse during a major earthquake. The proposed retrofit would strengthen the bridge to improve seismic performance and protect public safety.

The previous project proposed replacing the existing bridge with a new bridge. As the project advanced, the estimated construction cost increased to more than $80 million. The bridge replacement project would only have been eligible for limited funding through the Caltrans Seismic Retrofit Program, leaving a substantial funding gap that the County does not have available to construct the replacement project.

As a result, the bridge replacement project was discontinued, and Caltrans recommended a seismic retrofit of the existing bridge. The current retrofit is estimated at approximately $4.6 million in construction costs, substantially less than bridge replacement, while addressing the primary goal of reducing the risk of bridge collapse during a major earthquake.

The previous project proposed replacing the existing Bohemian Highway Bridge with a new bridge located just west of the existing structure. The new bridge would have included a wider roadway and new bicycle and pedestrian facilities, and construction was anticipated to occur over approximately three construction years. That replacement project was discontinued in 2023.

The current project would retain the existing bridge and seismically retrofit it to reduce the risk of collapse during a major earthquake. The current project has a smaller construction footprint and is anticipated to take approximately four to six months to construct. The existing bridge cross section would remain substantially unchanged, meaning the wider bicycle and pedestrian improvements proposed as part of the previous project are not part of the current retrofit project.

Because the project has changed from a bridge replacement to a smaller seismic retrofit, Caltrans and Sonoma County are revalidating the existing environmental documents to confirm they remain applicable to the revised project. A new environmental review is not anticipated. However, certain topics, such as Section 4(f) and community impacts, will be updated as needed to reflect the current project.

The community provided input during the development of the previous bridge replacement project, including feedback that informed the alternatives considered at that time. For example, the 2020 bridge alternatives analysis notes that a public survey showed a preference for a steel arch bridge over a steel truss bridge.

Information obtained through the previous outreach remains part of the project record and continues to inform the County’s understanding of community concerns. The previous outreach focused on a replacement bridge, including concepts such as wider bicycle and pedestrian facilities. Those improvements are not part of the current seismic retrofit project.

The current project is also using previous environmental studies and information about community and recreational resources as part of the re-evaluation of the revised project. However, because the project has changed substantially, the proposed environmental findings for the current retrofit will have a new opportunity for public review and comment before they are finalized.

No. The previously proposed bridge replacement project was discontinued in 2023. The current project would retain and seismically retrofit the existing bridge.

The proposed work includes:

• New reinforced-concrete support structures behind both bridge abutments
• Strengthening existing steel connections
• New steel ties connecting bridge spans
• New ties between the bridge and the supports behind the abutments
• Extensions to the bridge seats at both bridge abutments
• Cable restrainers connecting the bridge superstructure and piers
• Restoration of pavement and embankment disturbed during construction 

The current project is a retrofit of the existing bridge, rather than construction of a new bridge. The existing bridge cross section would remain, and the approach roadway work would be limited to the existing roadway width. The bridge would substantially retain its existing overall appearance and roadway cross section.

Yes. The bridge is anticipated to close to traffic during construction, which is currently expected to last approximately four to six months. During the closure, traffic would be detoured via Moscow Road and State Route 116.

The project team is developing a Traffic Control Plan to minimize disruption and maintain access to nearby homes and businesses. The County will also coordinate with fire, law enforcement, ambulance, transit, and other service providers before construction to plan for emergency response and temporary transportation changes.

Vehicles would be detoured using Moscow Road and State Route 116 while the Bohemian Highway Bridge is closed. The current detour map identifies the full route as approximately 7.35 miles. The full detour route is expected to add approximately 15 minutes of travel time, depending on traffic conditions.

Construction is currently anticipated to begin in summer 2028 and last approximately four to six months. The schedule is preliminary and may be refined as design and construction planning advance.

Construction of the new support structure behind the southern end of the bridge would require a temporary closure of the River Boulevard/Bohemian Highway/Main Street intersection for approximately one to two months. During this period, local traffic would be detoured via Bohemian Avenue, Bohemian Highway, Fir Road and Main Street.

The project team is working to minimize disruption and maintain continuous access to nearby homes and businesses, subject to temporary traffic controls. Additional details about the intersection closure, traffic management and construction phasing will be refined as design progresses.

The current traffic planning calls for continuous access to businesses and residences, subject to temporary traffic controls and the temporary intersection closure associated with work at the southern abutment.

Before construction, the County will coordinate with fire, law enforcement, ambulance and other emergency-response providers regarding the bridge closure, detour routes, construction schedule and incident response procedures. The Traffic Control Plan developed for construction will identify emergency-response routes and communication procedures.

Sonoma County Transit routes serve the Monte Rio area. Because the bridge would be closed, temporary rerouting or stop relocation may be necessary. Final arrangements would be coordinated with Sonoma County Transit and documented in the Traffic Control Plan.

While the bridge will be closed to vehicle traffic during construction, the project team is focused on maintaining safe pedestrian and bicycle access where feasible. The sidewalk is expected to be intermittently closed for approximately one to two months to accommodate construction activities. During these closures, temporary access and traffic-control measures will be developed to minimize disruptions to pedestrians and bicyclists.

Public access to the river and beach areas will be maintained during construction, except within designated construction, staging and safety exclusion areas.

Big Rocky and Sandy Beaches would experience temporary construction-related use, with fencing, barriers, signage or similar measures separating construction and public-use areas. Dutch Bill Creek Beach is not proposed for construction access or staging.

Temporary construction activity is currently anticipated at portions of Big Rocky Beach and Sandy Beach, as well as the River Boulevard and Main Street site. Koret Park, Riverfront Meadow and the Rio Theater are not proposed for construction, staging or access use under the current project.

The current proposal would use existing paved circulation areas at the Monte Rio Fishing Access as a temporary contractor access route. No staging, material storage, equipment parking, grading or permanent construction is proposed there. Recreational access is intended to remain available.

Yes. Approximately 30 parking spaces in the Big Rocky Beach Parking Lot are anticipated to be temporarily unavailable during construction. The County is coordinating measures to maintain recreational access, with parking details to be refined as staging plans are finalized.

Yes. Construction will temporarily generate noise from activities such as pile installation, concrete work, grinding, and temporary shoring. Much of the construction will occur near the bridge abutments, set back from the beach areas, so noise impacts are expected to be concentrated near these work areas.

Most construction activities are anticipated between 7:00 a.m. and 7:00 p.m., with no work on holidays and limited weekend work between 9:00 a.m. and 5:00 p.m. with prior approval. No permanent noise changes are anticipated after construction is complete.

No, not under the current project scope. The retrofit would retain the existing bridge cross section. Bicycle and pedestrian improvements presented during earlier community workshops were associated with the discontinued bridge replacement project, not the current seismic retrofit.

The existing bridge would remain in place with its current general roadway configuration. The retrofit is being designed to reduce the risk of collapse during a major earthquake.

Yes. The County will provide opportunities for the community to learn more about the current seismic retrofit project, including a public open house where community members can learn about the project, ask questions, and share input with the project team. Project information and updates will also be made available through the project website as the project progresses.

The draft Section 4(f) documentation is now available for public review. The proposed finding addresses temporary construction impacts to Big Rocky Beach and Sandy Beach, including beach access and parking.

Community members are encouraged to review the documentation and submit comments by December 10, 2026. Comments may be emailed to Samuel.Baumgardner-Kranz@sonomacounty.gov or shared at the November 10 community meeting.

See the Public Comment Opportunity: Section 4(f) Review section above for additional details and the document link.