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Marin County

Call to Action: Support Opening the Alto Rail Tunnel for Cyclists and Pedestrians

It would provide a safe, fast, and level route between Mill Valley and Corte Madera/Larkspur

By Marin County Bicycle Coalition

3:37 PM PST on February 10, 2026

Rendering from “Open Alto Tunnel”

The Marin County Bicycle Coalition sent out the following email blast and web post about an opportunity for cyclists to renew the push to reopen the Alto Tunnel between Mill Valley and Corte Madera. Streetsblog urges Marin residents and cyclists who like to bike there (which probably describes everybody on two wheels) to lend their support.

With the new year still young, we’ve got resolutions on the brain. Specifically, two city council resolutions we are working to see passed in Marin County. 

In December 2000, the City Council of Mill Valley and Town Council of Corte Madera both passed official resolutions supporting the effort to reopen Alto Tunnel and rehabilitate it for bicycle and pedestrian use (see those resolutions here and here). While those resolutions are not expired, they are now a quarter-century old. MCBC is asking the councils to renew these resolutions and reaffirm their commitment to an open Alto Tunnel. 

We hope that you will join us at the Mill Valley City Council on February 17th and the Corte Madera Town Council on March 3rd.

Click here to sign up to give a public comment!

The Background

MCBC’s campaign to open Marin’s abandoned rail tunnels to bicycle and pedestrian travel is as old as our organization. Our original goal of opening the two tunnels in Central Marin celebrated a huge success in 2010, with the opening of the Cal Park Hill Tunnel (our founding Executive Director Deb Hubsmith spoke at the ribbon cutting). However, despite several important studies completed on the Alto Tunnel in the 2010s, that project has stalled out. 

Map showing proposed Alto Tunnel connection linking Corte Madera and Mill Valley along the North-South Greenway."
Map showing the location of the Alto Tunnel

The tunnel, when opened, would connect directly to miles of already existing, highly utilized multiuse pathways in Mill Valley, Corte Madera, and Larkspur, extending nearly seamlessly into the Ross Valley and San Rafael. Although the project itself would be run by the County of Marin, local support is critical.

Electric Multiple Units once ran in Marin County through the Alto Tunnel. Photo: Northwestern Pacific Railroad Historical Society.

In 2000, both of the adjoining towns passed resolutions supporting the project, with reasonable caveats that the project be fully studied and that they not bear the cost of constructing the project (much of the funding for a project like this, as with the Cal Park Hill Tunnel, would come from federal sources). Due to the age of those resolutions, they are no longer treated as meaningfully representing the will of these two jurisdictions, leading to reluctance to act at the county level. 

Open Alto Tunnel’s Work

MCBC and Open Alto Tunnel speak at the Marin County Board of Supervisors
MCBC and OAT at the Marin Board of Supervisors

Over the past several years, MCBC and our partners at the volunteer group Open Alto Tunnel have done a great deal to raise the profile of the project. This includes collecting over 2,000 signatures from Marin County residents supporting Alto Tunnel reopening,  and presenting them to the County Board of Supervisors. But due to perceived lack of will at the local level, even that huge show of support has not shaken things loose.

Days of Action

We plan to present our petition, highlighting the hundreds of Mill Valley and Corte Madera resident signatures, to the councils in those two cities. Our primary request is that the councils update their 25-year-old resolutions and reaffirm their support of the project, with all necessary caveats. We will provide draft resolutions to this end, which they can adopt in part or in whole.

What we need from you is your voice speaking in support of the project. Too long have our leaders dawdled on this project, complaining about the project costing too much while failing to apply for any grant funding to advance it; decrying traffic on US-101 while opposing a project that would take 2,000 car trips off the road every day. 

What You Can Do

Click here to sign up to give a comment at the February 17th Mill Valley City Council Meeting (a Tuesday, unlike their normal meetings) or the March 3rd Corte Madera Town Council Meeting (also a Tuesday).

You can sign up to write an email, give a live comment via Zoom (Corte Madera only), or show up in person. The latter will be the most impactful!

When you come in person, we’ll give you a green “Open Alto Tunnel” t-shirt to wear, so that you can show support even if you are unable to give public comment (just see us at the end to give it back). 

We hope to see you there on February 17th and March 3rd – we’re counting on you! Don’t forget to sign up!

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