Highway 101 Interchange and Approaching Roadway Study
Accessing Highway 101 in Marin is a major source of congestion on local roads, which reduces the connectivity of communities across Marin. Some of the interchanges have had long-standing visions for improvements that have not yet been planned in detail. The interchanges vary in age; many of them were built in the 1950s and 1960s and have not been altered in meaningful ways to meet current and future demands of vehicles, transit, bicyclists, and pedestrians.
The Transportation Authority of Marin (TAM) has completed a study of twelve Highway 101 interchanges to identify a program of near- and long-term projects to improve safety and operation for vehicles, transit, bicyclists, and pedestrians, allowing smoother travel to, from and across Highway 101 and local roads.
The following factors were examined for each interchange:
- Existing infrastructure
- Transit routes and intermodal connectivity
- Weekday AM & PM peak period congestion
- Crash type and severity
- Environmental constraints
Based on the results of the study, three interchanges were prioritized to advance to the Project Initiation Document (PID) phase. A PID is required prior to developing an environmental document to advance the project further.
A Project Initiation Document (PID) is the starting point for a transportation project. It explains why the project is needed, outlines the basic scope and schedule, and provides a rough cost estimate. The PID helps decision-makers determine if the project should move forward into planning and environmental review.
In short, the PID is the first step to get a project officially recognized and considered for funding.
Three Interchanges have been prioritized to advance to the Project Initiation Phase:
Twelve interchanges were selected for the study based on input from stakeholders, including jurisdictional partners and the public, during the development of the Transportation sales Tax Expenditure Plan. Each represents significant access for adjacent communities along Highway 101.
The results of the Highway 101 Interchanges and Approaching Roadway Study shed light on ideas to improve the twelve interchanges. Download the Highway 101 Implementation Plan to learn more about the prioritization process and possibilities for future implementation.
For the three interchanges prioritized to advance, TAM is actively collaborating with Caltrans, Marin County’s local jurisdictions, transit agencies, and other key stakeholders in the Project Initiation Document (PID) phase to develop equitable strategies for implementing these improvements.
The Highway 101 Interchange and Approaching Roadway Study is funded through Measure AA – the re-authorization of the 1/2-Cent Transportation Sales Tax, approved by voters in 2018. The Expenditure Plan allocates 3% of the revenue from the sales tax, estimated to generate $25 million over the 30-year period of the Measure. The funding will be used to create the initial studies of 12 interchanges and will leverage regional, state and federal funds for a program of improvements to local road interchanges on Highway 101 in Marin.
Targeted Project Schedule
- Dec. 2025: Project Initiation Document Completed
- Early 2026: Alternative Reduction Workshops
- Late 2026: Initiate Environmental Studies
- Late 2029: Final Environmental Document(s) Approved
- 2029/30: Begin Design of the Preferred Alternative for one or more of the Interchanges
Dan Cherrier, PE, Project Manager
415-226-0829