Your help is needed, volunteer today! Ramping Up Efforts to Reopen Alto Tunnel

Friends of the Alto Tunnel / FOATFor the task of reopening Alto Tunnel, you’ve got some great allies on your side. Friends of Alto Tunnel (FOAT) have been working to get it reopened once and for all. FOAT is a coalition of pedestrians, bicyclists, and people of all physical abilities dedicated to reopening the former railroad tunnel between Mill Valley and Corte Madera as a safe, non-motorized route suitable for users ages 8 to 80+.

The Alto Tunnel, a critically  important bicycle and pedestrian connector between Corte Madera and Mill Valley, provides the only safe, flat and completely separated from traffic route between central and southern Marin.

Though more experienced cyclists can skillfully negotiate the challenge of using the roadway, there is presently no way to travel between Mill Valley and the rest of the County to the north by biking or walking without making the steep and difficult climb over Horse Hill or Camino Alto while navigating traffic and unsafe conditions.

Since the 1970s, the County has had plans for a North-South Greenway along the Northwestern Pacific Railroad right-of-way, spanning Marin County from North to South, providing access to transit centers, businesses, schools, and town centers. A well-used multiuse pathway extends for three miles from Sausalito through Mill Valley leading to the south portal of Alto Tunnel. Another pathway extends from the north portal through Corte Madera and Larkspur, connecting the Larkspur Ferry Terminal, the Cal Park Tunnel, and bike and pedestrian facilities and communities to the north. The Mill Valley to Corte Madera Bicycle and Pedestrian Corridor Study estimates 850,000 to 1.85 million annual users of Alto Tunnel. It’s no wonder FOAT are working so hard to get this vital community asset reopened!

Reopening the Alto Tunnel – in addition to improving safety and relieving traffic congestion by providing a non-motorized mobility option to local residents – is also critical to the completion of Marin’s North-South Greenway. Supervisor Kate Sears has said that she “appreciates how important the connection is to Marin County residents, is keenly aware of neighborhood concerns and looks forward to getting information about feasibility and costs to better inform the dialogue.”

History: So why was Alto Tunnel closed in the first place?

Northwestern Pacific Railroad built Alto Tunnel in 1884 utilizing timber supports. Several engineering reports state that the timber supports are now in an advanced state of decay. The Tunnel experienced a collapse in 1981, destroying portions of a home. In an effort to slow further collapse, the north end was lined and plugged with low-strength concrete and the engineering reports state that the Alto Tunnel is subject to continuing collapse, putting homes, roads, and major water mains at risk. If the Tunnel is not reconstructed, it is estimated that it will cost $11.5 million (2009 dollars) to abandon the Tunnel by backfilling it. With such a high price tag to taxpayers just to stabilize and abandon the Tunnel, which only benefits the adjacent land owners, FOAT argues (and MCBC agrees) that the money should be spent to reopen Alto Tunnel for everyone’s use, enjoyment and safety for generations to come!

The Famous Alto Tunnel Parade FloatThe Mill Valley to Corte Madera Corridor Study cost estimates for the Alto Tunnel and path range from $40 to $50 million. But, these numbers were based on a $21 million cost estimate with 2% escalation, a 35% cost contingency, an additional 20% accuracy allowance, and an additional $15 million for “Non Construction Project Cost.”

An accurate cost estimate will depend on the results of a long awaited geotechnical investigation led by the County of Marin and scheduled to be conducted this summer. For comparison, the similar SMART tunnel between San Rafael and Terra Linda was recently rehabilitated for only $4 million.

The County of Marin’s Alto Tunnel Property Ownership Study released in November of 2015 concludes that the County holds all necessary rights to construct and operate a public pathway/trail along the old railroad lands with the exception of two sections retained by the Railway within the portal. The Railway has previously offered to transfer its rights to the County. Reopening the Tunnel will necessitate the purchase of an easement under the side yard of the property at the south portal. Upon completion of the Tunnel, the side yard will remain as it is now, but the home on that property and the homes on adjacent properties will be stabilized.

In other words, what are we waiting for?! Let’s get Alto Tunnel reopened as soon as possible; Join FOAT today! You can start by liking the FOAT Facebook page. There are several upcoming events requiring many volunteers, including Bike to Work Day on May 12, Bike to Shop Day on May 21, and several summer festivals and parades. Check the FOAT Facebook page for more upcoming events. For more information on how you can get involved and to volunteer, please contact FOAT Steering Committee Chair, Don Herzog, at


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