Widening Highway 101 in Petaluma

Part of the Marin-Sonoma Narrows Project to build Carpool Lanes between Novato and Windsor

                                                                                                                                                                                                                                                    

PETALUMA - Caltrans is widening Highway 101 in Petaluma between Lakeville Highway (Route 116) and Corona Road by adding a carpool lane in each direction.

Upon completion, Highway 101 will be three lanes in each direction, including the new northbound and southbound carpool lanes. Ghilotti Construction is the contractor on the $78 million project. 

In November 2021, Caltrans opened the northbound carpool lane connecting it to existing HOV lanes, creating an uninterrupted HOV lane between the Marin-Sonoma border and downtown Windsor, a distance of nearly 30 miles.  

The $122 million construction project was built with $85 million from Senate Bill 1, the Road Repair and Accountability Act of 2017. The balance of the funds, nearly $37 million, comes from Sonoma County.  

Caltrans and the Sonoma County Transportation Authority worked in partnership on the project. 

The project includes building three soundwalls along the corridor to reduce noise for project neighbors next to the recently widened roadway.  

One of the difficulties of building the project has replacing the Petaluma Overhead, a section of elevated freeway north of E. Washington Street where the freeway passes over the SMART railroad tracks. 

With limited right of way in which to work, Caltrans temporarily moved traffic lanes to the median or the outside shoulders, creating enough room to demolish parts of the old bridge and then build a new, wider bridge, section by section.    

The process was repeated numerous time on both the northbound and southbound lanes: moving traffic to the left or right, demolishing a portion of bridge, then rebuilding it - a section at a time. 

At the northern end of the project where the freeway once traveled at ground level, Caltrans rebuilt the freeway as a bridge, which will allow the City of Petaluma to build an extension of Rainier Avenue that will pass beneath the freeway.