In a few places around the world--such as downtown London--drivers pay higher tolls for entering city centers at peak rush hour. The idea of "congestion pricing" is to reduce traffic and pollution by giving drivers an incentive to travel at off-peak times. Now a professor at the University of Texas at Austin has shown how a complex extension of this idea could greatly speed up rush-hour traffic flow throughout an entire network of highways and secondary roads in a U.S. metropolitan region. Using a computer model of driver behavior on the freeway system around the cities of Dallas and Fort...