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Project Description

Marin-Sonoma Narrows
Project Map

US 101 is the only continuous north/south route through Marin and Sonoma Counties and, therefore, is the principal route for local and interregional travel serving commercial, recreational, and commute traffic. Consequently, Caltrans has proposed a project that will:

  • Meet the needs of existing and forecasted travel demand to 2030
  • Improve AM/PM traffic congestion
  • Reduce HOV user delay for vanpools and express buses
  • Address physical deficiencies to improve safety:

  •      - Increase visibility (sight distance)
         - Improve drainage to address reoccurring flooding
         - Provide wider shoulders for emergencies

To achieve this, the MSN project area will be upgraded from an expressway to a freeway consistent with the freeway segments north and south of the MSN project area. This upgrade will involve the addition of interchanges. Interchanges will improve safety by:

  • Providing controlled access to US 101 from a number of roadways and driveways that currently intersect US 101. Interchanges will be accessed via a new frontage road system.
  • Allowing vehicles to accelerate/deaccelerate on the interchange ramps instead of on the freeway itself.
  • Providing continuous pedestrian/bicycle access between Novato and Petaluma with a combination of Class 1 and Class 2 bicycle paths.


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