Marin-Sonoma Narrows project costs climb as work goes on

All lanes of a Highway 101 widening project between Marin and Sonoma have been open since late September, but construction isn’t over and costs are creeping up.

Since the final phase of the Marin-Sonoma Narrows project got underway in 2022, inclement weather and unplanned work have challenged the crews, according to the California Department of Transportation. The last phase, called the “MSN B7” project, installed carpool lanes on 3.5 miles between Novato and the Sonoma County line.