Congestion takes place in the two dimensions of the road network.   Making use of the third dimension could be a means of relieving congestion.   Helicopters are noisy, expensive, energy intensive and elitist.   Tunnels are also expensive, but they serve mass transit and can get cars out of the surface environment.   I’ve been keeping my eye open for analyses of tunnelling fundamentals, hoping to get a sense of the prospects for cost reduction through new technology.   I’d welcome being pointed to sources by readers of this blog.

One slightly improbably place to find an account of modern tunnelling techniques is the New Yorker magazine of 15 September.   A long article focuses on the German firm of Herrenknecht AG, the largest maker of tunnelling machines in the world, with nearly a thousand machines burrowing under almost every continent.   The biggest current project is the Gotthard Base Tunnel in Switzerland, which will take road traffic 35 miles through challenging geology deep under the Alps.   One tunnelling machine got stuck after hitting a pocket of hydrothermally disintegrated stone.   It took five months work to free it.   As a consequence of this kind of problem, the project is five years late and $3bn over budget.

The New Yorker article is a piece of high quality reportage, not an economic or technical analysis.   Nevertheless, one can get a sense of the costs and uncertainties that seem inescapable in tunnelling.