Superhighway – Superhoax

Just finished reading Superhighway – Superhoax by Helen Levitt. Although written in 1970, and exclusively about the American Experience of how highways got built, there are a lot of themes that are very relevant to the situation in Quebec today.  The events leading up to the decisive 1956 legislation establishing the creation of the Interstate Highway system are very well documented and make for very sad reading…

Any of this sound familiar?

  • The need for a new highway is based upon traffic models that show increasing traffic which often is caused by previous road expansion projects.
  • Politicians having already made up their mind that the highway project is going ahead – citizens are invited for public consultations to discuss minor cosmetic elements only but not the question of whether it should be built in the first place.
  • The powerful roadbuilding lobby (concrete, asphalt, gas, cars) testifies to the legislators that this road system is necessary but they are unbiased and only concerned for the economic progress of the country.

She provides an excellent example of Parkinson’s Law adapted for traffic (page 258) when a new expressway opens between the downtown business district and outlying suburban areas.

Assume that the total number of commuters and automobile owners remain constant.  The following changes occur: For all auto commuters, the opened expressway results in reduced peak-hour traffic congestion on many previously existing streets as large numbers of commuters switch to the new expressway.  Gradually the time required for commuting on the expressway rises as more cars fill it, unit peak-hour congestion increases; whereas the time required on alternate routes falls.  When the two become identical, equilibrium is restored.  While rush-hour level on the alternate roads is now lower, rush-hour level of congestion on the expressway almost always exceeds its designed optimal capacity.  Assume the new road is designed to move 6000 cars an hour at 50 mph.  At optimum operating time, 6000 cars are traveling at 50 mph, but this is faster than speeds on alternate roads, so other will enter the expressway because of this speed advantage and more will join until speeds on all routes are identical.

Thus the net effect is that the new expressway is as congested as before but the net travel time may be slightly quicker. This is even before considering the new sources of trip generation (houses, businesses, etc..) that are subsequently built to take advantage of the new reduced trip time into the city.

Building highways for peak travel requirements is a never-ending loop of capacity expansion followed by capacity utilization.

Although this book was written in 1970, its quite sad to realize that its message wasn’t heard (then nor now).

1 comment so far

  1. Bianca Wirth on

    Yes, we should get rid of all of our roads and freeways. Then there will be no traffic congestion or traffic for that matter!


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