Engineers Lay Out Costs of Reopening Alto Tunnel to Bicyclists
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.
"Opening the Alto Tunnel has been a long-time goal because it represents the last link in what could be a 90-mile bike trail from Cloverdale to the Golden Gate Bridge," said Andy Peri, a spokesman for the Marin County Bicycle Coalition (MCBC).
"One of our big concerns is the assumptions in the cost estimates," Peri said. In addition, the estimate of riders drew numbers on the Corte Madera side and Mill Valley side then halved them. "Why not use a range of numbers in the report, or include a recent study that found bike ridership has doubled in the last decade?" he said.
Liz Muller, whose Corte Madera home is atop the tunnel, said reopening the tunnel would "totally change the neighborhood. People like to walk their dogs and chat and you can't do that with bikes zipping by." She worried about years of construction noise and the risks of a tunnel collapse during construction.
But the head of MCBC, Deb Hubsmith, challenged the cost estimates. She said the report used Cal Park Hill Tunnel costs as a baseline, even though Cal Park, also a rail tunnel is twice as wide and will reopen in 2010 as a shared path with a commuter train line.
The lower range of the Alto Tunnel cost should be $22 million, not $40 million, she told Craig Tackaberry, assistant director of Marin County Dept. of Public Works. She also argued that the report fails to outline the estimate cost of $11.5 million the county may need to spend to stabilize the tunnel to protect nearby homes, whether it is reopened or not.
Blake Rothfuss, tunnel engineer from Jacobs Associates, defended his calculations. He said no one has been inside for 38 years, but he relied on an engineering report from that time, known costs for removing ballast from the current Cal Park Tunnel project and tunnel renovations in the Pacific Northwest with similar rock formations.
The county is accepting public comments on the draft feasibility study until January 11th and may choose to complete one, two or all of the projects, adopt partial improvements or shelve them.