New research shows we don't need new roads to reduce traffic in metropolitan regions--just creative tolls. The results above show how traffic speeds would improve on the highway network around Dallas and Fort Worth, TX, under a scheme of "credit-based congestion pricing," according to Kara Kockelman, a civil engineer at the University of Texas at Austin. Vehicles would be monitored with radio frequency identification (RFID) or GPS technologies that would track where and when they were driven. Drivers would get a fixed monthly allotment of credits, which they'd "spend" on tolls that would vary according to mileage and location. Tolls would be as high as 20 cents per mile, for bottleneck stretches at peak times, but drivers would pay real money only if they'd used up their credits. The benefit: traffic up to 25 miles per hour faster during rush hour. At least, that's what Kockelman's computer model concludes after analyzing such factors as trip frequency and the value drivers place on saving time. The idea is under study; implementation would take years and would have to address privacy concerns.