MONTE RIO, CA., 11/2/26 — Sonoma County will hold a drop-in open house Tuesday, Nov. 10, on its plan to strengthen the 1934 Bohemian Highway Bridge in Monte Rio against earthquakes. The work would close the bridge to traffic for four to six months, starting in summer 2028 under the current schedule.
The open house runs from 5 to 7 p.m. at the Monte Rio Recreation and Park District’s community center, 20488 Highway 116. There’s no formal presentation. People can stop by anytime to see project information, meet the Sonoma County Public Infrastructure project team, ask questions and give feedback, according to the county’s invitation.
A retrofit, not a new bridge
The county had planned to replace the bridge, also known as the Monte Rio Bridge, with a new, wider one just west of it that would have included bicycle and pedestrian improvements.
It dropped that plan in 2023. By then the estimated construction cost had risen to more than $80 million. Money from the Caltrans Seismic Retrofit Program wouldn’t have covered a replacement, leaving a funding gap the county says it doesn’t have the money to close.
Caltrans recommended retrofitting the existing bridge instead. Construction on the retrofit is estimated at about $4.6 million.
The roughly 770-foot bridge carries Bohemian Highway over the Russian River. It doesn’t meet current seismic design standards. Engineering analysis found weaknesses that could raise the risk of collapse in a major earthquake, the county says.
The retrofit would add new reinforced-concrete supports behind the abutments at both ends of the bridge, steel ties connecting the bridge spans, longer bridge seats at both abutments and cable restrainers connecting the deck to the piers.
The bridge would keep its current width and overall look. The bike and pedestrian improvements shown at earlier community workshops belonged to the dropped replacement project. They aren’t part of the retrofit.
Caltrans and the county are revalidating the environmental documents from the replacement project. The county doesn’t expect a new environmental review.
Closure and detour
Construction is expected to begin in summer 2028 and last about four to six months. The county calls the schedule preliminary.
The bridge would be closed to traffic the whole time. Drivers would detour on Moscow Road and Highway 116, a route of about 7.35 miles that the county expects to add about 15 minutes, depending on traffic.
Building the new support behind the south end of the bridge would also close the intersection of River Boulevard, Bohemian Highway and Main Street for about one to two months. Local traffic would be detoured on Bohemian Avenue, Bohemian Highway, Fir Road and Main Street.
The bridge sidewalk is expected to close off and on for about one to two months. The county says it will try to keep pedestrian and bicycle access where it can.
Sonoma County Transit stops near the bridge may be moved or rerouted. The county says it will coordinate the closure and detours with fire, law enforcement and ambulance services before construction starts.
Most work would happen between 7 a.m. and 7 p.m. No work on holidays. Limited weekend work, between 9 a.m. and 5 p.m., would need prior approval.
Beaches and parking
Construction would temporarily use parts of Big Rocky Beach and Sandy Beach, which the Monte Rio Recreation and Park District manages. Most of the work would be near the bridge abutments, away from the main beach areas. The county expects the beaches to stay open except in fenced work and safety areas.
About 30 parking spaces in the Big Rocky Beach lot would be unavailable during construction.
Based on those impacts, the county is proposing a “de minimis” finding under Section 4(f) of the U.S. Department of Transportation Act, which protects public parks and recreation areas from federally funded transportation projects. The finding would mean the project won’t harm the recreational use of the beaches once steps to avoid, minimize or offset impacts are taken into account.
The county is taking public comments on the proposed finding through Thursday, Dec. 10. Comments can be emailed to Samuel.Baumgardner-Kranz@sonomacounty.gov or given at the open house. The draft Section 4(f) memo is posted on the project website, sonomacounty.gov/monteriobridge.
People can join the project’s email list by writing to EngagePI@sonomacounty.gov with “Monte Rio Bridge” in the subject line.