The high cost of installing and maintaining such systems has restricted their coverage to limited stretches of highway. "For state transportation agencies such as Caltrans, tapping into the vast network of cell phones on the road could one day reduce costs of investing in expensive infrastructure to obtain traffic information ... This will greatly expand the coverage of traffic information services so motorists can better plan their trips right on their cell phones." GPS-based systems can pinpoint a car's location with an accuracy of a few meters and calculate traveling speed to within three miles per hour, according to the researchers. Full Article at NBC 11 San Francisco