Highway 101 Widening in Petaluma

Widening Highway 101 in Petaluma

Project is part of the Marin-Sonoma Narrows Project to build carpool lanes between Novato and Petaluma


                                                                                                                                                                                                                                                                   Petaluma Widening Project Map

PETALUMA - Caltrans is widening Highway 101 in Petaluma between Lakeville Highway (Route 116) and Corona Road by adding a carpool lane in each direction on the 3.3 mile section of freeway.  

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 $122 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 last major milestone for the project will come in late July 2022, when Caltrans opens the southbound carpool lane. At that time, motorists will experience the full benefit of the project, as only minor construction work remains. 

The widening project was funded with $85 million from Senate Bill 1, the Road Repair and Accountability Act of 2017. The balance of the funds, nearly $37 million, came from Sonoma County.  

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

Included in the project are four new soundwalls to reduce noise for project neighbors adjacent to the recently widened roadway.  Caltrans has built an auxiliary lane 

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.    

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. 

A bike/pedestrian path travels beneath the Petaluma Overhead alongside the SMART tracks.  The path was closed early in the project to allow rooms for construction and to protect the public from hazards in the construction zone.  Caltrans plans to reopen the multi-use path this fall, upon completion of construction. 




    Existing and Proposed

The Marin-Sonoma Narrows Project 

The Petaluma Widening Project is one of 13 projects of the larger Marin/Sonoma Narrows widening project to add a carpool lane in each direction of Highway 101 between State Route 37 in Marin County and Corona Road in northern Petaluma.

Only two roadway projects remain on the Marin-Sonoma Narrows, including this project. 

The final project will begin in late July 2022, which will add carpool lanes between Novato and the Marin Sonoma County border.