Caltrans Scheduled to Open HOV Lanes on Northbound, Southbound US-101 in Final Week of September as Part of Marin Sonoma Narrows Project

Schedule: Work continues Sunday, Sept. 28 from 8:30 p.m. until 7 a.m.

Marin County - Caltrans is scheduled to open the long-awaited, continuous HOV lanes (third lanes) on Northbound and Southbound US-101 as part of the Marin Sonoma Narrows B7 project in the final week of September.

The lanes are scheduled to open as early as Monday, Sept. 29 or Tuesday, Sept. 30 after striping operations conclude on Sunday, Sept. 28. All work is weather dependent.

This striping work will remove merges on Northbound US-101 (just north of Atherton Avenue) and Southbound US-101 (south of Kastania Road), which will open three continuous lanes through the Marin Sonoma Narrows B7 project.

Work is scheduled to continue at night on Northbound US-101 from Sunday, Sept. 28 through Saturday, Oct. 4 between 8:30 p.m. and 7 a.m. the next mornings.

Lanes are scheduled to be closed on Northbound US-101 in that time period. At least one lane will be open for traffic.

The San Antonio Road on- and off-ramps on Northbound US-101 are scheduled to be intermittently closed during that same time frame. Consecutive ramps will not be closed at the same time.

Detour for on- and off-ramp closures on Northbound US-101

• San Antonio on-ramp closure: Drivers must enter on US-101 southbound at San Antonio Road, exit at the Atherton Avenue off-ramp and then re-enter US-101 northbound.
• San Antonio off-ramp closure: Drivers must exit at Petaluma Boulevard South/ Kastania Road, enter US-101 southbound, and exit at San Antonio Road

All work depends on weather. Daytime access will be available for motorists.

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.

This is the last remaining High Occupancy Vehicle (HOV) lane construction project as part of the 16-mile US-101 Marin-Sonoma Narrows (MSN) program. This project will complete and allow continuous HOV lanes on US-101 from Sausalito in Marin County to Windsor in Sonoma County.

For 24/7 traffic updates, please visit 511.org: https://x.com/511SFBay For real-time information, visit Caltrans QuickMap: https://quickmap.dot.ca.gov Follow us on X: https://x.com/CaltransD4 Or call 1-800-472-7623, 1-800-427-ROAD for state highway conditions statewide.