The Privatization of Roads and Highways - Ludwig von Mises Institute

74 The Privatization of Roads and Highways
Additional accommodation creates additional traffic. The opening
of a freeway designed to meet existing demand may eventually
increase that demand until congestion on the freeway
increases the travel time to what it was before the freeway
existed. 41
A definitive explanation is given by Bish and Kirk:
If people would really like to travel at uncongested speeds during
the journey-to-work hours, just how much additional highway
investment would be necessary? If one looks at engineering
forecasts for freeway travel before the freeway opens and
the actual freeway travel shortly after opening, one is continually
amazed at the lowness of the peak-hour forecasts relative
to actual travel. Far in advance of the time predicted, the new
freeway has traffic beyond “capacity” and is congested again.
Why does this happen over and over again? There are essentially
two reasons. First, there is usually more than one highway
route to work that takes approximately the same amount
of time. This is because if any route were significantly quicker,
travelers would shift to that route, increasing its congestion
while reducing congestion on the formerly slower route until
times were equalized. Thus, when a new route opens up, traffic
using a variety of former routes will switch to the new route
until travel time on the new route is equalized with time on
adjacent routes. If former routes have been city streets and the
new route is a freeway, equilibrium may not be established
until freeway traffic is very slow and congested. However,
travel time will be less on both the new and old routes because
of the increase in highway capacity.
But these gains, even in reduced travel time, if not in reduced
congestion, are likely to be dissipated. Bish and Kirk continue:
A second reason why new routes congest prior to forecast is
simply that when transportation capacity increases and peakhour
time decreases, fewer drivers will take the trouble to beat
41 Dyckman, “Transportation in Cities,” p. 143. See also Owen, The Metropolitan
Transportation Problem, p. 109.