It'll be shut down in both directions at Sears Point near Sonoma Raceway. The detour requires drivers to take Highways 121, 12 and 29 just to get around. The closure starts overnight Saturday and isn't expected to reopen until 11 a.m. Sunday.
"It's not going to be pretty," said Erin Giordana.
Giordana from Sonoma was gassing up, ahead of what could be a busy weekend on the roads.
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"It's going to be gridlock. Cars will stack up. This center part gets clogged on a regular day," Giordana said.
Caltrans will close an 11-mile stretch of Highway 37 for SMART train track repairs, starting early Saturday morning through around midday Sunday.
"For all of us Sonoma residents, it's going to be an interesting weekend to say the least," said Garrett Walker.
The 32-hour closure will happen between 121 at Sears Point and Highway 29 in Vallejo.
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A detour will take westbound drivers the long way around, north on 29 to Highways 12 and 121.
Eastbound drivers will take the same route in reverse.
"Highway 37 is already a mess. I assume 12 and 121 will become a nightmare," said Walker.
"You can expect a much longer drive. It's pleasant, but you might want to go on Sunday after 11 a.m. when the road is reopening," said Jeff Weiss from Caltrans.
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That's not an option for wedding parties and tourists that booked venues at Cline Family Cellars months ago.
"May is our busiest month of the year. We have emailed everyone with reservations to let them know about the road closures happening," said Kyle Ritchie, tasting room manager at Cline Family Cellars.
Caltrans says 47,000 cars travel Highway 37 on a daily basis. This weekend all that traffic will have to find a new route.
"So either plan on taking the detour or travel the route on a different day," Weiss said.