County Looks to Dive into Deeper Study of Land Around Alto Tunnel

Save for a recent dustup over whether or not Mill Valley would mention it in its updated General Plan, little has happened with the Alto Tunnel – the 129-year-old former railroad tunnel that has been closed since 1971 – since the county allocated $600,000 in 2011 to further study the possibility of re-opening it as a flat bicycle-pedestrian connector between Mill Valley and Corte Madera.

That's about to change, as the Marin County Board of Supervisors is expected to approved Tuesday a contract (attached) for an engineering firm to study the land around the tunnel, and specifically who owns it, in the hopes of homing in on cost estimates that have ranged from $40 million to as high as $60 million.

Project opponents have cited the high end of those estimates as exorbitant for a county government to spend on a bicycle-pedestrian path.

The contract, for $68,920 with Santa Rosa-based BKF Engineers, calls for the firm to do an aerial survey of the site and compile property ownership records.

At issue are the property boundaries of those who own homes above and around the tunnel, specifically a few that have been built since the tunnel closed in 1971.

How the possible re-opening of the tunnel would impact those landowners has become central to the controversy surrounding the issue.

While the 2010 Mill Valley to Corte Madera Bicycle and Pedestrian Corridor Study indicates that the tunnel can be built with no disturbance to homes above the tunnel, members of the Scott Valley Neighborhood Association have raised vocal opposition about the potential damage caused by and the liability surrounding the excavation.

Also at issue are property easements attached to the tunnel itself. Property owners in the area have suggested that those easements reverted back to nearby landowners when the tunnel closed, meaning that the county would have to purchase new easements, a likely costly and time-consuming endeavor.

In addition to the Alto Tunnel, the county’s 2010 study, which cost $225,000, also looked at possible improvements to the active Camino Alto/Corte Madera Avenue and Horse Hill/Casa Buena connectors, both of which could be improved for a fraction of the cost but are much hillier than the tunnel.

The Alto Tunnel is 16 feet wide, 20 feet tall and 2,172 feet long. It is longer but narrower than the 1,100-foot Cal-Park Tunnel, the former railroad tunnel that was built at the same time as the Alto Tunnel and re-opened in Dec. 2010 as a bike-ped connector between San Rafael and Larkspur. That project cost $25 million.

The Alto Tunnel stayed open until 1971. A cement plug filled 125-feet at one end in 1975 and in 1981 a southern portion collapsed, leaving engineers to guess at the true difficulty of reconstruction.

After the land survey work is finished, the county intends to spend another $420,000 on a geotechnical study to get a better sense of the cost of the excavation and reconstruction of the tunnel. That study will likely occur in mid-2014, at a time when the water table is lower so workers don’t encounter a tunnel mostly filled with water from the winter rains, officials said.

County officials estimate that between 850,000 and 1.85 million people would use the tunnel annually. Bike advocates, particularly the Marin County Bicycle Coalition, have been vocal proponents for the project, and in 2011 gathered more than 2,500 signatures in support of the connector.

“We are, for the most part, just waiting for these studies to be completed to get a better sense of the issues and costs involved with the tunnel,” said Andy Peri, the coalition’s advocacy director. “We’ll see what happens from there.”