Streetsblog San Francisco

Addressing a crowd of more than 100 people Wednesday, engineers said it could cost $40 million to $52 million to reopen the crumbling 125-year-old railroad tunnel between Mill Valley and Corte Madera for cyclists.

The nearly half-mile-long Alto Tunnel was just one of three bike route improvement plans outlined in a newly released study, part of the Nonmotorized Transportation Pilot Program.

The other two routes are well known to any cyclists who've ridden north of Mill Valley. An existing path over Horse Hill skirts Highway 101 and twisty Camino Alto climbs 450 feet of hill above the tunnel and is a popular segment of weekend training loops for many riders. Improvements on these two routes would cost roughly $5 million each.

But some cyclists shy away from Camino Alto because of its narrow lanes, speeding cars and afternoon traffic jams.

Cyclists have dreamed of reopening the Alto Tunnel as the last barrier to a nearly flat connector between the two towns and a key link to a greenway stretching from the Golden Gate to Cloverdale.

The 16-foot-wide tunnel would link existing bike paths on both sides of the hill. Southern Pacific Railroad sealed the 2,172-foot passageway in 1971, dooming its redwood supports to rot in the stagnant, moist darkness. 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.

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A large and divided crowd turned out last night in Marin County to help decide whether the long-neglected Alto Tunnel between Mill Valley and Corte Madera should be reopened to cyclists.

County planners stressed the workshop was intended only to gather community input on three possible routes as part of a $225,000 study that will be concluded this fall. But emotions shifted into high gear as cyclists cited reasons to restore the railroad tunnel that’s been decaying over the last four decades.

“The handwriting is on the wall. It’s only a matter of time,” said David Hoffman, planning director for the Marin County Bike Coalition. “There aren’t any issues with the tunnel that can’t be resolved.”

Like much of the existing bike network in Marin and Sonoma counties, the 16-foot-wide tunnel was built by the railroads. It opened in 1884 as redwood forests were being leveled to support urban sprawl in San Francisco. The passage was sealed in the 1970s, and portions have collapsed as its 12-by-14 redwood beams rotted in the dank, stagnant air trapped beneath the mountain. The southern end crumbled in a rainstorm 28 years ago. Several large portions have been filled. The north end is plugged with 125 feet of cement.

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Cycling enthusiasts have long dreamed of reopening the rotting, 125-year-old Alto Tunnel as a key link in a greenway stretching from the Golden Gate Bridge to Cloverdale. Now they may get their chance, as the county's Non-motorized Transportation Pilot Program begins a $225,000 study of three routes between the two southern Marin towns.

The tunnel between Mill Valley and Corte Madera is the focus of a transportation workshop tomorrow night in Marin County. 

The other two routes are well known to any cyclists who've ridden north of Mill Valley: an existing bike path over Horse Hill by Highway 101 and the twisty Camino Alto, which climbs to about 450 feet on the hill above the tunnel. Neither route is pedestrian-friendly, and many cyclists shy away from Camino Alto because of its narrow lanes, fast cars and afternoon traffic jams.

The 16-foot-wide tunnel would link existing bike paths on both sides of the hill. Southern Pacific sealed the 2,172-foot passageway in 1971, dooming its 12-by-14 redwood supports to rot in the stagnant, moist darkness. The southern entrance collapsed during a rainstorm in 1981 and several other portions have been filled to protect the homes on the hilltop.

“People are very, very excited about the tunnel," said Andy Peri, a spokesman for the Marin County Bike Coalition who predicted dozens of cyclists will show up. "One woman just called me and told me she’s bringing all five of her children from 7 to 17 years old.”

Reopening the tunnel won't be easy. Neighborhood residents, who've enjoyed the solitude of hiking along the overgrown approaches, are organizing against the project. “It is a [public] right-of-way and it is not their private property, but a lot of people would like to see it left alone. Some people have a fear that homeless people would be living up there," said Peri.

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