By requiring car drivers to pay a fee to drive in a city at peak hours, congestion pricing reduces traffic and raises money that can be used to support public transit—both worthy goals.

Yet congestion pricing has dubious environmental value. Traffic jams, if they're managed well, can actually be good for the environment. They maintain a level of frustration that turns drivers into subway riders or pedestrians.

Jay H. Walder, the man appointed this week as chairman and chief executive officer of New York's Metropolitan Transportation Authority, helped design London's congestion pricing scheme. New York certainly has plenty of congestion. At the busiest times of the day, cars on side streets in midtown move so slowly that they appear almost to be parked, and taxi passengers often watch in dismay as pedestrians outpace them and disappear into the distance. Mr. Walder has said he isn't planning to bring up congestion pricing again for New York, but the fact that he was chosen for the job suggests that it's at least a possibility.

In 1949, only 3% of American families owned more than one car; in 2001, for the first time, the number of cars in the United States exceeded the number of licensed drivers. The resulting traffic jams look like an ecological disaster. And they are one, but not for the reasons that people usually assume.

Congestion isn't an environmental problem; it's a driving problem. If reducing it merely makes life easier for those who drive, then the improved traffic flow can actually increase the environmental damage done by cars, by raising overall traffic volume, encouraging sprawl and long car commutes. A popular effort to curb rush-hour congestion, freeway entrance ramp meters, is commonly seen as good for the environment. But they significantly decrease peak-period travel times—by 10% in Atlanta and 22% in Houston, according to studies in those cities—and lead to increases in overall vehicle volume. In Minnesota, ramp metering increased overall traffic volume by 9% and peak volume by 14%. The increase in traffic volume was accompanied by a corresponding increase in fuel consumption of 5.5 million gallons.

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