Engineers Lay Out Costs of Reopening Alto Tunnel to Bicyclists

_1.jpgDeb Hubsmith of MCBC addressing Public Works Asst. Chief Craig Tackaberry (far left). Photo by Tom Murphy.

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.

"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).

_3.jpgPhoto by Tom Murphy.

Participants spent an hour sounding off with concerns about the tunnel or critiques of the study, which cycling enthusiasts say over estimated costs but under estimated the potential ridership. By contrast neighbors expressed concern over construction noise, potential tunnel collapse during construction and disruption of the neighborhood by adding hundreds of cyclists speeding through the tunnel.

"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.

  • Thanks for the great article!

  • CBrinkman

    Please weigh in cyclists – I for one want that tunnel so badly. We visit family in Corte Madera and although I can handle that hill, I hate the car traffic on it. It really makes me think twice about biking when we go to visit family – sometimes we drive instead just to avoid dealing with cars on Camino Alto.

    Public comments and input will be accepted at the Public Workshop #2, and by email ( or by mail for 30 days after the workshop until January 11, 2010.

  • ZA

    Certainly worth doing, but worth doing well. Structural safety, lighting, enforcement, and a decision of how to safely share the facility between cyclists and pedestrians is imperative.

  • Tom Murphy

    When you consider the $6 billion (and more?) being spent to retrofit the Bay Bridge, it seems silly not to spend $60-70 million reopening the tunnel AND turning both Horse Hill and Camino Alto into better bike routes. Both the existing routes are unfit for families with children; only the relatively flat tunnel route could accommodate younger riders, the disabled and casual recreational bike riders. The tunnel would be used to access commute routes into the city and allow people north of the Alto hill to get to the Mill Valley rec center. It would reduce traffic on the hairpin turns of Camino Alto, which is unwelcoming to all but the bravest cyclists, and provide a bike route over the hill during commute hours when the narrow auto lanes are bumper-to-bumper with cars. This isn’t a case of building one or the other. All three make sense to encourage people to get out of their cars. Thanks to SF/SB for keeping us informed on this…it’s really important!

  • i agree it’s worth the money. and i also agree it’s worth doing well — we have to allow safe and dignified access for walkers and bikers. time to plan for the future. better late than never.

  • Patrick

    Horse Hill is a horrible option.

    with all the knowledge of the detrimental effects of inhaleing car exhaust, coupled with the increased breathing rate of cyclist, why would they consider running a bikeway immediatly adjacent to an often gridlocked highway?

    It is one thing if the road is there, and its the best way through, but to spend money on improviments as a human powered transit route? That is rediculous.

    I spent several years commuting up Tunnel Road in Oakland, and the worst part of the route was the lower section before the traffic jam entered the Caldecott tunnel.

    In the interest of public health, all human powered transit routes should be located away from automobile traffic whenever there is the option.

  • Why is an estimate even taken seriously when nobody has been inside for 38 years! For all we know it could be completely dry and well preserved.

    As a recreational cyclist, this hill is just one of many annoyances while riding through Marin. Coming from a completely separated bike path from Sausalito or Corte Madera makes the change all the more jarring.

    The work done for the SMART train includes other bike/pedestrian tunnels, so why would we avoid this project?

  • tNOB

    After reading this, I feel this woman’s concerns about the tunnel collapsing are backwards. If this thing is sitting there rotting away, shouldn’t she be concerned if they didn’t renovate it? Does this call for a new term… NUMBY, Not Under My BackYard?

  • I don’t know. I’ve read about this project before from here on the East Coast and at $40 to $52 million to repair this tunnel might it be better to see if it could serve some sort of mass transit purpose?

    That’s “ALOT” of cash to spend on a half mile bike/ped project. Tunnels of greater length on Pennsy rail-trails were secured for much less money (but were in better shape). Even as a staunch cycling advocate, I think it may be wiser to spend that amount of money elsewhere.

    What about going up and over the hill in a straight line? The tax map overlay on Google Maps would seem to indicate some sort of ROW between all the houses (see

  • Alexei

    I’ve ridden the route a number of times and this project would be amazing. No denying that $50 million is a whole lot of money, though.

    I have the same reservations about the Bay Bridge bike path proposal.

  • Matthew Sessions

    To educate all readers here regarding the vertical terrain of the 3 proposed routes, take a look at page 2 here:

    Horse Hill is adjacent to Hwy 101 and parts of the route have grades of more than 15%. Camino Alto is a 330′ hill (or Category 4 climb for those familiar with race rankings). It’s literally not possible for young and elderly cyclists to use these routes.

  • Yeah I checked the topo too. Going straight over via the possible ROW would be steep but short, require less overall vertical gain and would be mostly closed to vehicular traffic.

    Again, it’s just a thought from 3000 miles away.

    The Bay Bridge should definitely have a bike/ped path. Unlike this tunnel, there are no other reasonable walkable/bikeable alternatives without the use of transit which is not always available. What would you Marin folk do if you couldn’t bike or walk across the Golden Gate?

    Either way, best of luck and my best regards with this project!

  • I actually like the climb over Camino Alto (and the downhill) precisely because it’s a bit of a workout and to focus on something Jeremiah mentioned: there is a much wider range of users (kids with training wheels and their families and pretty much anyone who isn’t wearing spandex) on the Sausalito-Mill Valley bike/pedestrian trail than ever use Camino Alto or Horse Hill.

    Comparing Camino Alto (and Horse Hill) to the Alto Tunnels is apples and oranges even after you consider how many additional bike/pedestrians would use the Alto Tunnel who would never even consider Camino Alto. Estimates in the draft study for daily usage (bike and pedestrian) after improvements at:

    Alto Tunnel: 2,329
    Camino Alto: 1,233 (up from a current 981)
    Horse Hill: 451 (up from a current 414)

    Now if I’m doing my math right (and someone please check this) improving Horse Hill would get about 10% more use, Camino Alto (with sidewalk) would have 26% and using that improved Camino Alto figure as a baseline the Alto Tunnel would have 137% more users.

  • Avery St. Clair

    I regularly hike this path, and instead of the tunnel use an over-the-hill route just west of the tunnel alignment. Part of it is dirt path so not well suited to some bikes. And as noted above, steep and narrow at times. Alto Tunnel must be reopened. Alternatives are either impractical (adding more and more lanes to 101) or simply not going to happen (light rail over the Golden Gate). It’s time for this project to move forward.

  • Avery St. Clair

    Sorry; EAST of the tunnel alignment. Coach Road / Fire Road / Sausalito Street / Buena Vista. Not optimal but there’s very little traffic.


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