Alto Tunnel bike and pedestrian plan is an expensive pipe dream – Marin Independent Journal

Cyclists ride on Lomita Drive after exiting the Horse Hill bike path in Mill Valley on Tuesday, Aug. 1, 2023. (Alan Dep/Marin Independent Journal)

The Marin County Bicycle Coalition’s regular campaigns to rebuild the half-mile-long Alto Tunnel make the proposal sound deceptively simple by mislabeling it as “reopening,” when the reality of the project is much more complex.

I prefer the term “reconstruct” because the proposal is actually a new bore. The tunnel was partially filled with concrete to stabilize it after the collapse of its southern section in 1982, and according to the most recent study in 2017 (which involved lowering cameras into the central section), the entire central section has also collapsed, compromising its structural integrity.

In all discussions surrounding the tunnel, the biggest obstacle has been the cost, not only of the reconstruction itself, but also of acquiring and developing the various sections of rights of way needed to provide perfect access to the tunnel portals. Proponents have consistently underestimated these costs and downplayed the impact of such a huge project on the residential areas that have sprung up around the route since the tunnel was closed.

There are two houses above the tunnel portals. In my informed opinion (and the opinion of several other experts I have consulted), both would need to be cleared to stabilize them before the bore is completed. One of these properties is a true restricted property with an expensive house on it, to which the county has no access rights whatsoever; to acquire those rights, expropriation would be necessary.

In addition, there are several properties on the Corte Madera side where the county has no ownership or control of the rights of way, and there are two properties in the middle of the tunnel that are still owned by the Union Pacific Railroad, which will not release them without full compensation.

Bicyclists who want to travel between Mill Valley and Corte Madera have two alternatives: the Camino Alto bike path, which could be widened, and the Horse Hill multi-use trail, which could be re-evaluated. County consultants have estimated the cost of optimizing these routes to be a fraction of the cost of rebuilding the tunnel.

As far as I can tell, the tunnel proposal has only lukewarm political support. It faces strong neighborhood opposition on both the Mill Valley and Corte Madera sides. The Horse Hill route improvement appears to have political support but no neighborhood opposition.

In 2009, county consultants estimated the total cost of rebuilding the tunnel to be about $60 million. In 2017, after the aforementioned study of the collapsed tunnel interior was completed, they estimated the cost to be about the same. However, to make this possible, they developed a new plan that involved reducing the width of the tube from the tunnel’s original width of 16 feet to 11.5 feet. I suspect this is simply too narrow to allow for safe two-way traffic for bikes and pedestrians.

Since 2009, construction, labor and material costs have increased dramatically. The cost of properly reboring the tunnel 16 feet wide – after acquiring expired easements and blocking off lots and stabilizing or acquiring the homes above the portals – could easily cost over $125 million today.