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 nalysis is finding that traffic congestion is getting
worse in major American metropolitan areas because of sprawl
and its impact on driving habits. Using new data from the Texas
Transportation Institute, the companion analysis by the Surface
Transportation Policy Project finds that neither population growth
nor too few roads are to blame for the rise in traffic jams.
 While
the population in all 68 metro areas studied grew by 22 million
since 1982, the increase in driving has crowded the roads with
the equivalent of 70 million more drivers. For example, in Washington
DC, a population increase of 765,000 feels like an increase of
more than 2 million on the roadways, because residents are driving
77 percent more.
"This
analysis shows just why drivers have felt so besieged by ever-increasing
traffic. Sprawl is making just about everyone drive farther and
more often, and that fills up the roads." said Roy Kienitz,
Executive Director of STPP. The paper, Why Are the Roads So
Congested? A Companion Analysis of the Texas Transportation Institute's
Data on Metropolitan Congestion, was provided by the Surface
Transportation Policy Project.
Sixty-nine
percent of the increase in driving from 1983 to 1990 was due
to factors influenced by sprawl, such as longer car trips and
a switch to driving from walking or transit. Population growth
itself was only responsible for 13 percent of the growth in driving.
STPP found
that every 10 percent increase in the highway network results
in a 5.3 percent increase in the amount of driving, over and
above any increases caused by population growth or other factors.
This confirms other research on induced travel, the phenomenon
in which increased road capacity generates additional traffic.
In addition, road-building has not been an effective congestion-fighting
measure: the metro areas that added the most highway space per
person have seen congestion levels rise at a slightly higher
rate than areas that added few roads per resident.
"It turns
out that the most common response to congestion, road building,
is just making things worse," said Kienitz. "We don't
need more of the same: we need new solutions that give people
a way to avoid traffic jams."
STPP's full
analysis is available at www.transact.org.
The Texas Transportation Institute provided STPP with early access
to its data. To view the Texas Transportation Institute's report,
please go to mobility.tamu.edu. 
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transact.org.