SAN FRANCISCO — Drivers heading between San Francisco, Marin, Sonoma, Napa and Solano counties face a major North Bay disruption beginning Wednesday night as Caltrans starts a sequence of closures on State Route 37.
The first two closures affect westbound SR-37 only from 7 p.m. to 4 a.m. Wednesday and Thursday nights. The larger shutdown begins at 10 p.m. Friday, Oct. 23, when Caltrans plans to close both directions between Mare Island in Vallejo and Sears Point until 5 a.m. Monday, Oct. 26.
When exactly is Highway 37 closed?
- Wednesday, Oct. 21: westbound closed 7 p.m.–4 a.m.
- Thursday, Oct. 22: westbound closed 7 p.m.–4 a.m.
- Friday, Oct. 23 at 10 p.m. through Monday, Oct. 26 at 5 a.m.: both eastbound and westbound closed between Mare Island and Sears Point.
Caltrans says all work is weather-dependent and warns travelers to expect significant delays and increased travel times.
What is the eastbound Highway 37 detour?
Caltrans directs eastbound drivers toward northbound SR-121, then SR-12/SR-121 through the Carneros area, continuing to SR-12/SR-29 before using the connector back to eastbound SR-37.
That route pushes traffic onto roads that can already be busy on a fall weekend. Anyone driving from Marin or Sonoma toward Vallejo, I-80 or points east should leave additional time and check live traffic before committing to the corridor.
What is the westbound detour?
Westbound traffic is directed onto northbound SR-29, then westbound SR-12 and southbound SR-121 before returning to westbound SR-37 near Sears Point.
For San Francisco travelers, the closure matters most for trips that would normally use SR-37 as the east-west link across the North Bay — including routes between Marin/Sonoma and Napa/Vallejo/Solano. Alternate routes may add substantial distance.
Why is Caltrans closing the highway?
Caltrans says crews will demolish median work and install temporary barrier so traffic can later be shifted. The agency then plans to raise portions of the eastbound roadway by about 3 feet to improve flood resilience and prepare for storm conditions.
The agency describes the work as emergency preparedness and is urging motorists to use alternate routes whenever possible. Before leaving, verify the closure status with Caltrans or 511 because weather can move the schedule.