The Wall Street Journal‘s recent special report, “The Future of Cities,” included an article on large road tunnels (“Boring Has Never Been So Exciting,” by Daniel Michaels). It celebrated the great improvement in cost-effective tunneling made possible by the invention and perfection of the tunnel boring machine (TBM). These amazing machines, now available in diameters exceeding 50 feet, have a massive rotating cutting head at the front, followed by a control cab and a whole train of support vehicles. Each TBM is custom built for that job, and many include the ability to install pre-cast concrete panels as the TBM moves forward, so the machine not only excavates but actually constructs the tunnel as it progresses.
I first learned about TBMs over a decade ago, via a video documentary on the building of the SMART Tunnel in Kuala Lumpur. That 6-mile tunnel used a 43 ft. diameter TBM. Its name stands for Stormwater Management And Road Tunnel, and that is exactly what it is. Most of the time, the tunnel handles road traffic on two decks, one for each direction of travel. When severe flooding is threatened, road service is suspended, and the tunnel becomes a massive flood-relief channel. Begun in 2003, it opened to traffic in 2007 at a cost of $515 million. It was financed via toll revenues, which it obtains via all-electronic tolling TBMs are being used in the United States, but mostly for water and subway tunnels. The only two roadway tunnels I’m aware of are the Port of Miami Tunnel and the Alaskan Way Tunnel in Seattle. The former was a big success, tunneling underneath a shipping channel in difficult soil conditions to link the port with the metro area’s expressway network. Procured as a design-build-finance-operate-maintain P3 concession, it was finished on-budget and nearly on time. Its purpose is mainly to shift large trucks and buses for cruise ship passengers off downtown Miami streets. Alas, the Seattle tunnel has been delayed nearly two years by a broken TBM cutter head, and only recently resumed tunneling. That sort of problem is an exception to the generally very good track record of TBM tunneling.
TBMs were pioneered by German and Japanese companies in the 1970s. Today’s leading TBM provider is Germany’s, which told the Journal reporter that it is providing TBMs for as many as 100 projects annually, up from about 20 projects a year 15 years ago. These machines permit tunneling to proceed up to 10 times as fast as traditional digging and blasting methods.
Major road tunnels are under way around the world, with the largest number of projects in China. One of the most dramatic projects is the Bosphorus Road Tunnel, connecting the two halves of Istanbul. TBM tunneling under the Bosphorus Strait was completed last August, and the double-deck roadway and other systems are currently being constructed, with opening to traffic set for early 2017. The $1.25 billion project is a toll-financed DBFOM P3 concession. The tunnel will cut the current car and mini-bus travel time from 1.5 hours to just 15 minutes. Other current road tunnel projects include the following:
Twinning of the existing El Melon tunnel in Santiago, Chile, being done as a toll concession;
Malaysia’s $1.55 billion bridge and tunnel to link Panang Island to the mainland; Hong Kong’s $1.9 billion Tseung-Lam Tunnel; and, The $1.5 billion, 8.7-mile Agua Negra Tunnel linking Chile and Argentina.
I’m aware of only two U.S. highway mega-tunnel projects in the planning stages, both in Los Angeles. One would fill in the long-missing link in the Long Beach Freeway (I-710) via a tunnel beneath South Pasadena. The other is a proposed tunnel beneath highly congested I-405 in the Sepulveda Pass, estimated to cost between $7 billion and $9 billion. It would accommodate both toll lanes and a rail transit line.
Even with TBMs, tunnels are costly propositions. But given the difficulty of adding missing links to existing expressway systems in dense urban environments, such tunnels may well be the only realistic way to add much-needed capacity. People expect to pay tolls to use major bridges and tunnels, so much of the cost can be covered by toll revenues, which also make it possible to finance tunnel projects up-front. If such tunnels can now be built even in high water table areas like South Florida, they should be part of transportation planners’ tool kits in all major metro areas.
(Reprinted from the May 2016 issue of Surface Transportation Innovations)