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Just tunnels baby, just tunnels

written by andy on

Elon Musk’s unveiling of a tunnel is causing quite a stir in the transit advocacy community. Musk promised a high speed network of cars moving in a tunnel but only demonstrated a normal car moving on a rough surface inside a tunnel at a much lower speed.

While we can fairly question the wisdom of putting cars in a tunnel instead of trains, as well as the technical feasibility of a vehicle traveling more than 100 mph, there are things that transit advocates and planners can take away from. Musk was able to build a tunnel at a very low cost.

Part of the reason for the low cost, in comparison to transit projects, is that the tunnel is just plan tunnel, without stations, tracks, wayside power, signaling systems, and maintenance facility. Also with rail, you will need a longer line (beyond the gap corridor) to make the service usable and allow for connections.

Can we deliver transit with tunnels without the high cost associated with traditional subway constructions? I think it is possible.

I think the concept of bus subways should be visited. Bus subways are only needed in gap corridors and otherwise buses use regular streets outside the gap.

We already have buses running on electricity and with physical guides. The only thing that prevented tunnel buses running in high speed is a vehicle control/signaling system that has long been available to rail, but autonomous vehicle technology may address that.

Image result for o-bahn city access project
Guided buses in Adelaide, Australia.

Basically, build a pair of tunnels for guided buses strictly in the gap corridor where tunnels are necessary. Forget the stations and the rest. Run buses on streets from either end of the tunnels. Compared to a single rail line, a bus network would allow for more point to point service with fewer transfers. This allows for an incremental transportation improvement with a limited infrastructure in place, and allows the cities to build-as-we-go.

The reality is that physical infrastructure is expensive. The bigger and more complex the system is, the more expensive it is to build and deliver. A rail subway system has many physical infrastructure: tunnels, stations, tracks, wayside power, signal system, maintenance facility.

Because of the large scope, both in geographical and infrastructure, it can easily take a generation to build a high speed rail system linking northern and southern California.

A guided bus system can go with plain tunnels with a simpler concrete pavement. Power can be delivered by battery. Autonomous vehicle technology can replace a physical track signal system. Buses would use surface bus stops and continue service on surface streets beyond the tunnels.

Such system can be useful to address the gap corridors, like the transbay corridor and the Sepulveda Pass, where additional transit infrastructure is desired and alternatives are limited. In both examples, tunnels can be built only for these gaps.

Bus tunnels can also address shorter gaps, such as between the Dumbarton Bridge approach and Downtown Palo Alto/Stanford University. For decades, the bridge and Downtown Palo Alto are linked by surface streets. While the corridor is only about 3 miles long, it can take 45 minutes to travel during peak times due to street congestion. Freeways and surface street widening are not viable because of NIMBY issues south of the 101 freeway and social justice issues north of the freeway. Residents on both sides of the freeway want less and slower traffic. While there’s a rail corridor, it doesn’t directly connect to Palo Alto. A connection to Palo Alto via the Caltrain tracks would put more trains on the over-burdened Caltrain corridor.

A stationless tunnel can connect the gap and make transit significantly more competitive and would have minimal impacts to the ground above, whether it is the low income North Menlo Park/East Palo Alto or the uber-wealthy Palo Alto. Buses can begin route from various points in the East Bay and end route in other locations on the Stanford campus. Buses can pick up from the train station and drop off at the Facebook campus.

The key to make this possible is a significant reduction in tunnel construction cost. We would be running more buses anyway, but a tunnel would reduce operating times and improve ridership.