Marin-Sonoma Narrows project continues in Marin County toward 2025 completion

Completion of the Highway 101 Marin-Sonoma Narrows widening project is in sight as work continues with an eye toward a summer 2025 opening.

The Marin-Sonoma Narrows B-7 construction project is ongoing with new ramp lighting and ramp metering work this month, which requires ramp closures on Southbound US-101 near Novato. In May 2021, the Metropolitan Transportation Commission provided $76 million in STP/CMAQ funding to help the overall $135 million segment move forward. 

This is the last remaining High Occupancy Vehicle lane construction project as part of the Narrows program, which will see 17 miles of carpool lanes in each direction through Marin and Sonoma counties, completing a total 50 miles of continuous carpool lanes in each direction, between Windsor and Richardson Bay.

MTC has long identified improvements to the U.S. 101 corridor in the North Bay as an important regional priority, including the Marin-Sonoma Narrows, where lanes narrowed from three to two creating bottlenecks. The work expands lanes from four to six, adding a carpool lane in each direction.

MTC has also contributed $15 Million in re-purposed federal earmarks, another $15.4 Million in STP funds and $23 Million in RTIP funds, and monies from the Prop 1B Corridor Improvement program, among other dollars to the overall widening project. Caltrans, the Transportation Authority of Marin and the Sonoma County Transportation Authority are partners on the project.