Wednesday, July 08 2009 @ 03:39 PM UTC
Contributed by: B' Spokes
One example is reducing traffic congestion by eliminating roads. Though our transportation planners still operate from the orthodoxy that the best way to untangle traffic is to build more roads, doing so actually proves counterproductive in some cases. There is even a mathematical theorem to explain why: “The Braess Paradox” (which sounds rather like a Robert Ludlum title) established that the addition of extra capacity to a road network often results in increased congestion and longer travel times. The reason has to do with the complex effects of individual drivers all trying to optimize their routes. The Braess paradox is not just an arcane bit of theory either – it plays frequently in real world situation.
Likewise, there is the phenomenon of induced demand – or the “if you build it, they will come” effect. In short, fancy new roads encourage people to drive more miles, as well as seeding new sprawl-style development that shifts new users onto them.
Of course, improving congestion is not the main reason why a city would want to knock down a poorly planned highway–the reasons for that are plentiful, and might include improving citizen health, restoring the local environment, and energizing the regional economy. More efficient traffic flow is just a wonderful side benefit.
Sound dubious? Here are several examples of how three cities (and their drivers) have fared better after highways that should never have been built in the first place were taken down.
CASE 1: Seoul, South Korea - Cheonggycheon highway
CASE 2: Portland, Oregon - Harbor Drive
CASE 3: San Francisco - Embarcadero Freeway
CASE 4: San Francisco - Central Freeway