The Alto Tunnel Study

The Alto Tunnel Study is an effort to gather information to determine whether it is feasible to reconstruct  the Alto Tunnel for future use by bicyclists and pedestrians. The County is the lead agency in partnership with and cooperation with the Town of Corte Madera and the City of Mill Valley.  To learn more about the study, click here.

On September 27th, a community meeting was held at the Corte Madera Community Center to discuss what was found inside the tunnel and the updated cost estimates. To view a video recording of that meeting, please click on the YouTube embedded video below. 

The video will remain on the Community Media Center of Marin (CMCM) Youtube page. CMCM serves Marin County with community, educational and governmental cable channels via Marin TV. Click here to go directly to their page.

NEW!!! Alto Tunnel Investigation and Cost Estimate Update - 2018

The Alto Tunnel Study collected information requested by policy makers and the community to help make an informed decision about whether to reconstruct the tunnel for potential future bicycle and pedestrian use, or if there is a need to fill and permanently close it at some future point.  The final report for the Alto Tunnel Study has been issued on the investigation of the interior reaches of the tunnel and the revised cost estimates.

The final report, appendices, and public comments received to date have been posted to the WalkBikeMarin website or you can view them by clicking the links below.  As always, you can find background documents on that page as well as on the 2010 Mill Valley to Corte Madera Corridor Study webpage here.  

• Alto Tunnel Investigation (Report Only)
• Appendix A: Site Photos
• Appendix B: 
  • Plan Views
  • 3D Tunnel Scan Plan & Sections
  • Cross Sections and Permanent Backfill Option
• Appendix C: Factored Construction Cost Estimates for Alto Tunnel
• Public Comments Received on Draft Study

What’s Next?
At this time, the County considers the Alto Tunnel Study complete and anticipates no further action or work by the County in their upcoming staff work program.

• Should you choose, you, your neighbors, community leaders, and elected officials may continue independent community conversations about the possible future of the Alto Tunnel
• Use the collective information on the website to help guide and inform decisions, if any, about the future of the Alto Tunnel  

The County of Marin thanks you for your interest and engagement during the preparation and completion of this important study of the Alto Tunnel.