Stephen Rees's blog

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

Big Dig pushes bottlenecks outward

with 5 comments

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

5 Responses

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  1. There’s absolutely no mention of the 2004 completion of the widening of US Route 3 which increased capacity by a lane in each direction between the New Hampshire border and the Boston area.

    And of course, they want to widen I-93 by two lanes in each direction in New Hampshire.


    November 16, 2008 at 4:46 pm

  2. Thans for this- more useful evidence against the roadbuilding projecs locally

    Andy in Germany

    November 16, 2008 at 10:51 pm

  3. Toronto still has a lot of streetcar lines – I doubt that the impetus for replacing the Bloor streetcar or the Yonge streetcar with subways was to free up space for cars. With the Yonge line it was due to overcrowding and a need for more passenger capacity.

    Ron C.

    November 17, 2008 at 10:58 am

  4. AS a side note, the article also provides an indication of what people expect to be “acceptable” traffic delays. Travelling 11 miles in 12 minutes equals a full on highway speed of 55 mph. For 25 minutes, that equals 26.4 mph or 42 km/h – that’s hardly a crawl.

    Ron C.

    November 17, 2008 at 11:05 am

  5. Toronto operates mostly non articulated cars (the TTC has about 50 articulated cars but they are very heavy and do a lot of damage on the tracks) and has little transit priority at intersections, which reduced capacity. Even with rather antiquated rolling stock the streetcars can move over 7,250 persons per hour per direction, per line, in peak hours. Using articulated cars would effectively double this!

    Malcolm J

    November 17, 2008 at 12:11 pm

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