Drivers who depend on Highway 12/121 through Schellville should plan ahead. Caltrans will close the stretch at the Arroyo Seco Bridge for the entire month of October. The shutdown begins at 12:01 a.m. Oct. 1 and runs around the clock until 5 a.m. Oct. 31.
Why it’s happening
The Arroyo Seco Bridge, built in 1923, has railings that no longer meet modern safety standards. Crews will remove the old barriers and install new ones that bring the bridge up to code. Because the bridge is narrow with no shoulders, Caltrans says it’s impossible to keep traffic flowing safely during construction. A one-month full closure is faster than nearly three months of one-lane controls.
Detour route
Traffic will be diverted onto a signed detour. Westbound drivers from Napa to Sonoma will exit at Napa Road, head west, then turn south on 8th Street East to rejoin the highway past the bridge. Eastbound drivers will take the same loop in reverse. Caltrans will post electronic signs, but locals know Napa Road and 8th Street East are small roads. Expect congestion and build in extra travel time.
Emergency planning
Caltrans worked with fire, EMS and law enforcement before locking in the plan. First responders agreed a shorter, full closure was safer and more efficient than a drawn-out partial closure. Emergency vehicles will also use the detour. The construction site will not be open to regular traffic.
What’s next
The Arroyo Seco Bridge is first. Nearby Yellow Creek Bridge on Route 121 is scheduled for similar railing work later this year or early in 2026. Both projects are part of a safety upgrade program.
What drivers need to know
- Closure dates: Oct. 1–31, 24/7
- Detour: Napa Road and 8th Street East
- Expect longer trips and delays
- Congestion likely during peak commute hours
Maps and updates are available through Caltrans District 4 and 511 Bay Area. For anyone moving between Napa and Sonoma, October will be a hassle. The payoff, officials say, will be safer bridges and smoother travel for years to come.
