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Reopening the Alto Tunnel: Frequently Asked Questions

Where is the Alto Tunnel Located?

The Corte Madera portal lies between Tunnel Road and Montecito Road, at the south end of the multi-use path. The Mill Valley Portal is north of Vasco Court, forming the dead-end of the Sausalito-Mill Valley Multiuse Path.

How Many People are Projected to Use the Alto Tunnel Annually?

The Mill Valley to Corte Madera Bicycle and Pedestrian Corridor Study estimates 850,000 to 1.85 million annual users.

Why Would the County of Marin Want to Restore Alto Tunnel?

Presently, only fit and skilled bicyclists can go between Mill Valley and the rest of the county without using motor vehicles. The Alto Tunnel will provide a safe and level non-motorized route suitable for all ages and abilities, and will significantly reduce traffic congestion and pollution. The tunnel will provide an emergency route for ambulances and service vehicles and an evacuation route when roads are gridlocked. Reconstructing the Tunnel will stop ongoing collapse and will stabilize adjacent homes and improvements. Since the 1970s, the County has had plans for a North-South Greenway along the former 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.

What Have Been the Experiences When Other Bicycle and Pedestrian Tunnels in the U.S. Have Opened?

The County of Marin commissioned a Rails to Trails Conservancy study of tunnels throughout the United States which have been opened to bicyclists and pedestrians. The report concludes that tunnels are overwhelmingly safe, that they are valued by communities, and that there is a trend throughout the United States to open more tunnels to non-motorized use. “Tunnels on Trails, A Study of 78 Tunnels on 36 Trails in the United States” covers issues related to: safety, liability, costs of tunnel restoration, construction, maintenance, and the impacts of tunnels on the existing transportation network and surrounding communities. The study also found that property values often increased, and that while all neighborhoods had concerns before the tunnels were opened, some of the most vocal opponents of the tunnels came to be the most frequent users and supporters of the tunnels once they were opened.

What Are Some Benefits of Restoring Alto Tunnel?

Reopening Alto Tunnel for bicycle and pedestrian use would:

Improve Safety: Currently, bicyclists and pedestrians have two choices for traveling between Mill Valley and Corte Madera, neither of which is safe or ADA accessible. The “Horse Hill Route” is a series of busy and dangerous roads connected by a very short and steep section of path next to the freeway. The route requires riding or walking on Tamal Vista Blvd., Madera Blvd., the dangerous Tamalpais Ave intersection, steep hills on Meadowsweet or Casa Buena Drives, Lomita Drive, and through the Edna Maguire School drop off and parking lot.

The Camino Alto Hill route is a steep, winding and busy road with only limited shoulder. There have been numerous bicyclists seriously injured on this road over the years.

Decreased Traffic Congestion: Reopening Alto Tunnel would create a straight, flat pathway that would be accessible to people of all ages and physical abilities. People would be able to commute to San Francisco, access the Manzanita Transit station, shop at businesses on either side of the hill, attend soccer practice and other after-school activities, go to the Mill Valley Community Center and pool, and commute to the College of Marin and the Larkspur Ferry Terminal. Many auto trips could easily be replaced with bicycle or pedestrian trips once the Tunnel is open.
Route for People in Wheelchairs: Opening Alto Tunnel would provide a socially-equitable transportation option for people in wheelchairs; there are two residential communities that support disabled people in the vicinity of Alto Tunnel.

Physical Health Benefits: The U.S. Centers for Disease Control and Prevention estimates that 300,000 Americans die each year due to complications associated with obesity and sedentary lifestyles, and that 67% of U.S. adults are overweight or obese. The CDC recommends 30 minutes of physical exercise, five times a week, for adults and states that replacing trips by automobile with walking or cycling is one of the best ways the get this exercise.

Environmental Health Benefits: The useful route provided by the Alto Tunnel will replace motor-vehicle trips, reducing air and water pollution.

Emergency Egress Benefits: There has been much attention placed on the slogan “Get Ready Marin” which urges residents to be prepared in the event of a disaster. The Alto Tunnel would provide an important emergency egress should there be a fire or other emergency.
Stabilization of Adjacent Properties: The Alto Tunnel is currently unstable (potentially endangering neighboring properties). Reconstruction will stop ongoing collapse and will stabilize adjacent properties and improvements.

What is the Condition of the Alto Tunnel Today?

The Alto Tunnel is 2,172’ long, 16’ wide, and 20’ high. It was built by Northwestern Pacific Railroad 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 south end was partially backfilled with pea gravel.

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.

The northern 170-feet was inspected in June, 2001 and determined to be in good structural condition. The Southern 350-feet was backfilled with gravel in 1982 and will have to be excavated and supported with a new concrete structure. The exact condition of the middle 1600-feet is unknown at this time; however, a geotechnical study has been funded to better determine the condition in this zone and is scheduled to be completed by the County of Marin sometime in 2016.

How Much Would it Cost to Reopen the Alto Tunnel and Make it a Part of the North-South Greenway?

The Mill Valley to Corte Madera Corridor Study cost estimates for the Alto Tunnel and path range from $40 to $50 million, but 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 the Geotechnical Investigation scheduled for 2016. For comparison, the similar SMART tunnel between San Rafael and Terra Linda was recently rehabilitated for only $4 million.

Would Funds to Open Alto Tunnel Take Away from Schools, Parks, Emergency Services, or Other Projects?

No. The funds that would be used to open the Alto Tunnel would be transportation project funds and competitive federal and state grants; they would not take away from schools, parks, emergency services, etc.

How Would Security and Maintenance be Handled?

Once the Alto Tunnel is opened, there will be annual costs to maintain and operate this facility. Some security measures that have been used in other tunnels, including the Cal Park Hill Tunnel between Larkspur and San Rafael, include: security cameras, police patrols, and lighting. These are likely the types of features that we would see if Alto Tunnel were reopened. Because the portals to Alto Tunnel enter and exit in Mill Valley and Corte Madera, cooperation and coordination among the towns and the County of Marin would be essential.

How Will Reopening the Alto Tunnel Affect Neighbors?

There are some neighbors near Alto Tunnel who enthusiastically want to see the tunnel reopened, and some who are against the project and have major concerns. It will be important to open up more of a dialog with the communities immediately near the portal. There are many ways to minimize any possible negative impacts that reopening the Alto Tunnel may have. Landscaping can create a visual barrier to the pathway, and sound mitigation can help to reduce any errant noise. Signs can be posted urging tunnel users to please be quiet and respect the neighbors. In addition, as with any transportation or development project, neighbors’ concerns must be weighed against the benefits of the project to the community at large. And, various forms of fences can be attractively constructed to separate the users from the neighbors who wish to have privacy.

Who Owns the Rights to the Alto Tunnel?

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 section 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.

Tunnel rehabilitation will not endanger or require removing any homes and no one will be displaced from their home. Tunnels are routinely constructed safely beneath existing buildings. By reconstructing the Alto Tunnel and replacing the existing rotting timber supports with steel beams, homes that are currently at risk of collapse will be stabilized.

Are There any Environmental Considerations?

All transportation projects have environmental considerations; the Alto Tunnel project will need to go through review under CEQA, the California Environmental Quality Act. If the County of Marin were to determine that they were ready to move forward with reopening the Alto Tunnel, the appropriate departments within the County of Marin would determine the type of environmental review necessary.

Overall, reopening the Alto Tunnel would produce significant health and environmental benefits for Marin County. People’s health would benefit from increased walking/jogging/cycling, and environmental benefits would be accrued from motor vehicle trip reduction. The existence of a flat, straight, car-free route would attract people who might otherwise walk or bicycle today, but are dissuaded due to the hills and current levels of automobile traffic on surface streets.

How Can I Help?

* Volunteer for Friends of Alto Tunnel public outreach events to help spread the word about the Alto Tunnel and to build support for reopening it.

*Attend public meetings regarding the Tunnel.

*Write letters to your elected officials expressing your support for reopening this widely beneficial community asset.

*Ask organizations that you’re involved with to write letters of support and/or to adopt a resolution of support for reopening the Alto Tunnel. Contact Friends of Alto Tunnel at friendsofaltotunnel@gmail.com to schedule a presentation before your organization to learn more about how to do this.

*”Like” Friends of Alto Tunnel on Facebook.

*Join our mailing list by inputting your information in the box to the right to receive the latest news and updates, calls to action, and ways in which you can get involved.

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