Stephen Rees's blog

Thoughts about the relationships between transport and the urban area it serves

Posts Tagged ‘Big Dig

Big Dig pushes bottlenecks outward

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Thanks to Patrick Condon (a native Bostonian) for this link.

For those of you who may not be aware of this project, a huge freeway tunnel has been dug underneath the centre of Boston, Mass. This is an old city by US standards and has had a pretty good transit system for a long time. The freeway was supposed to relieve traffic congestion – which it has, in downtown. Now drivers line up elsewhere, once again proving the aphorism that urban road expansion does not solve congestion, it just moves it someplace else.

A Globe analysis of state highway data documents what many motorists have come to realize since the new Central Artery tunnels were completed: While the Big Dig achieved its goal of freeing up highway traffic downtown, the bottlenecks were only pushed outward, as more drivers jockey for the limited space on the major commuting routes.

Ultimately, many motorists going to and from the suburbs at peak rush hours are spending more time stuck in traffic, not less. The phenomenon is a result of a surge in drivers crowding onto highways – an ironic byproduct of the Big Dig’s success in clearing away downtown traffic jams.

The worst increase has been along I-93 northbound during the evening commute. In 1994, before the tunnels were dug, it took, on average, 12 minutes at peak evening rush hour to go the 11 miles from the Zakim Bridge to the Route 128 interchange in Woburn.

Now it takes 25 minutes, double the time.

Which is the other aphorism. Traffic expands to fill the space available. More people are now trying to drive and it is taking them longer. It is known in the business as “induced traffic”. Not that the population has grown. All that has happened is that more trips are being made by car now. The same population drives more often and longer distances. The vehicle miles travelled have increased. That always happenms when you build more roads in urban areas or introduce traffic management schemes to improve vehicle flow. Indeed, cities like Toronto that had streetcars but replaced them with subways – thus freeing up more surface area for cars – saw traffic congestion worsen. Many European cities have abandoned what they called “pre metro” i.e. undergrounding of streetcar routes.

As Patrick remarks “of interest to all except Minister Falcon”

Written by Stephen Rees

November 16, 2008 at 2:30 pm