Mill Valley Road Work: SR 131 Sidewalk Project Underway, Major Interchange Construction Years Away

MILL VALLEY, Marin County — October 31, 2026. Two transportation efforts near Mill Valley are at very different stages. Caltrans’ State Route 131 sidewalk and curb-ramp improvements entered construction in September, while the Transportation Authority of Marin is still studying possible future changes at the Tiburon Boulevard/East Blithedale Avenue interchange.

SR 131: Work scheduled during the day

In an official September 24 update, Mill Valley said Caltrans began curb-ramp and sidewalk work on Route 131 during the week of September 21. The announced schedule is weekdays from 7 a.m. to 5 p.m., with limited delays expected during the fall. Paving is planned for spring 2027.

Caltrans is coordinating with Marin Transit and the school district to reduce impacts on buses. That coordination is not a guarantee that an individual trip will be free of delays. Travelers should check current route notices and observe any work-zone restrictions.

Tiburon/East Blithedale: Still a study

The separate interchange effort, led by the Transportation Authority of Marin, aims to consider congestion, safety and connections for people walking, biking, taking transit or driving. According to the city’s announcement, the authority was selecting consultants for preliminary engineering and environmental studies. Construction is not expected before 2033.

The projected timing means residents should not treat drawings, concept options or discussion of the interchange as an approved construction closure today. Design alternatives and funding may change during further study and consultation.

How to follow the work

The city’s transportation notice links separately to Caltrans for Route 131 and to the Transportation Authority of Marin for the interchange study. Residents can use those project pages for updates and potential opportunities to submit comments. For a trip on a particular day, a current traffic alert is more reliable than a general construction schedule.

Primary source: City of Mill Valley, “Transportation Updates: State Route 131 and Tiburon/East Blithedale Interchange,” September 24, 2026.

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