The Marin–Sonoma Narrows (MSN) project targets one of the most well-known bottlenecks on US-101 between Novato in Marin County and Petaluma in Sonoma County, a corridor long affected by daily congestion, limited transit benefits and aging infrastructure. The improvements aim to restore mobility and safety along one of California’s most vital north–south highways.
The project’s primary goal is to widen the highway by adding one high-occupancy vehicle (HOV) lane in each direction, creating a continuous carpool system through the North Bay. The upgrades improve HOV capacity, reduce delays, support higher-capacity travel modes and modernize the corridor. The route serves commuters traveling between Marin and Sonoma counties, including Novato, Petaluma, Rohnert Park and Santa Rosa, and links directly to the broader Bay Area economy. By relieving congestion and offering more reliable travel, the improvements support regional growth and reduce travel times for thousands each day.
“The coordination of funding, design and construction across multiple agencies allowed the project to advance in pieces while maintaining overall corridor vision,” said Ronald Sangalang, regional project manager for Caltrans…