Caltrans photo illustration for the planned new intersection of Highways 121 and 12 south of Sonoma. Highway 12, running north and south, will be realigned to a true T-intersection with 121. Fremont Road just to the north will become westbound only.

Caltrans this week began construction work on reconfiguring the intersection of Highways 12 and 121 south of Sonoma, putting a traffic light there and changing the habits of many drivers.

The project, which is costing $2.4 million for the construction, will realign Highway 12 and cause it to meet Highway 121 in a T-intersection. Now, the two highways meet at an angle.

Just to the northeast of the Highway 12 intersection, Fremont Road intersects with 121. Many, if not nearly all, drivers on 12 heading to Napa orĀ  beyond use Fremont to get to 121. But Caltrans is turning Fremont into a one-way, westbound road only, so all eastbound traffic will have to use the 12/121 intersection with the traffic light.

Caltrans spokesman Robert Haus said the changes were prompted by an higher-than-average accident rate at the intersection. With the shift to a T-intersection, he said, drivers will be able to better see approaching traffic.

This week, Caltrans has been narrowing 121 to one lane at night at 12 to allow crews to work on the project. Work will resume at 8 p.m. Friday, lasting until 5 a.m. Saturday, and Haus said that as the project moves along motorists can expect further one-way traffic control there.

Haus said the remodeled intersection should be completed in about six months.

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