Alto Tunnel News Update from the Alto Tunnel Campaign – Summer 2023

Tunnel? What Tunnel?

That was the question of many at the Mill Valley Memorial Day Parade when they saw the Friends of the Alto Tunnel tunnel float. Excitement was in the air as people who didn’t know about the tunnel learned that it connects Mill Valley and Corte Madera. Though it’s been closed for many years, the tunnel is just waiting to be reopened to complete Marin’s North-South Greenway! It would be a huge step toward creating one long, safe, easily accessible, bike and pedestrian corridor through Marin County for all to use and enjoy!

Since our campaign reboot in April, we’ve been busy! Read below to see what’s been going on and how you can get involved. 

Alto Tunnel Campaign Updates

Alto Tunnel Campaign Update June 2023

Outreach in the Community

The Friends of Alto Tunnel and MCBC staff attended the Earth Day Marin event hosted by Green Change, as well as Mill Valley’s Memorial Day Parade. At both, we had the famous Alto Tunnel float, where future users of the tunnel could run and roll through it. Feedback was overwhelmingly positive. Those familiar with the tunnel were happy to see progress being made, and many were excited to learn about it for the first time. Their typical response: “There’s a tunnel there? Of course, we should open it! Why would anyone be against it?”


To show that there are hundreds of times more supporters of the tunnel than opponents, we are collecting signatures for a petition, urging the Marin County Board of Supervisors to move the project forward. If you haven’t signed it, you can do that here. We are currently over 25% of our goal of 2,000 signatures in just two months! 


In addition to the petition, we are seeking partner organizations to add their names to the letter that will accompany the petition. These partners can be other advocacy organizations, environmental groups, businesses, or riding clubs. If you represent a group that is potentially interested in co-signing our letter, please note it in the petition above and email

How You Can Help

Re-Open Alto Tunnel

Click to enlarge

Event Volunteering

We’ll be pushing the float at the Corte Madera 4th of July Parade. If you want to help out in any way (assembling/disassembling the float, walking in the parade, handing out flyers), we’d be happy to have you! Please email and you’ll be connected with the event organizers.

Join Friends of Alto Tunnel

Friends of Alto Tunnel is the volunteer group supported by MCBC that organizes the campaign to reopen the tunnel. We meet monthly, typically on Zoom and occasionally in person in Mill Valley. If you want to learn more about the group, you can register for our upcoming Friends of Alto Tunnel Zoom Orientation. We want to give people the opportunity to learn about the group and get up to speed with our activities. That will be held on Thursday, June 29th from 6-7 pm. Register here.

The group’s next full meeting will be on Monday, July 10th at 3 pm. Register here.

For more information about the studies done up to this point, please visit the Friends of Alto Tunnel website at

We work hard to bring you the most up-to-date news about biking in Marin. We can only do this with your support. Consider making a donation today.

Support Us

sign-up for advocacy alerts

We will need your help winning these improvements! Please sign-up for advocacy alerts using the form below and we’ll tell you when/how to support our efforts.

members make it happen

We’re working to make Marin more bike-friendly for people of all ages and abilities. Are you with us?

Similar Articles

Get Involved in Re-Opening Alto Tunnel

The single most transformative project in Marin County would be the re-opening of the Alto Tunnel to bicycle and pedestrian travel. The tunnel, dug through the ridge between Mill Valley and Corte Madera by the Northwestern Pacific Railroad in 1884, was boarded up in 1975. But since the 90s, advocates have pushed to repurpose the Alto Tunnel, and other tunnels like it, for active transportation use, allowing people to bypass hills and avoid busy roads.

Update On The Great Redwood Trail

Few projects now underway in California capture the imagination like the Great Redwood Trail. A planned 320-mile multi use pathway connecting San Francisco Bay to Humboldt Bay, the GRT is steadily becoming closer to reality.