Marin Sonoma Narrows B-7 Project

The Marin-Sonoma Narrows (MSN) B-7 project continues to progress throughout 2024, leading to HOV lane completion scheduled for the summer of 2025.

The project reached another milestone on April 12, 2024, when traffic was shifted on US-101 in both directions from Novato near Olive Avenue to San Antonio Road.

Southbound traffic was realigned away from the temporary median lanes, into the newly constructed Southbound US-101 road section. That section has been raised to match the median that was opened in June 2023.

Northbound US-101 traffic was realigned into those same temporary median lanes now moving in the opposite direction, as the next phase of construction begins to reconstruct the old northbound road section.

Construction for the project includes widening US-101 to install HOV lanes for 3.5 miles along the northbound lanes from North Novato to the Marin, Sonoma line, and for 6.3 miles along the southbound lanes from De Long Avenue to the county line.  

On June 10, 2023, Caltrans diverted Southbound US-101 traffic onto new elevated lanes spanning San Antonio Creek to just north of Atherton Avenue in Novato. This was the first major milestone for the project.

Since then, the project has been working to reconstruct approximately four miles of the old Southbound lanes. The contractor repurposed roadway materials of the old US-101 to incorporate as base material for the new highway, saving time, money, and environmental resources.

To improve sight distance, the new road is as much as 10 feet higher than the old US-101 in some areas. Construction is ongoing in this stage to construct seven new retaining walls, widen the existing Franklin Avenue overhead bridge, and complete the approximately 93,000 cubic yards of earthwork.

Contact

Matt O’Donnell
Marin County Public Information Officer
Email: matt.odonnell@dot.ca.gov
Phone: (510) 852-5113