Traffic Management Traffic lights are key tools for regulating traffic How.They are not, however, perfect.Drivers exchange the traffic jams that would happen at unmanaged crossings for a pattern of stop-go movement that can still be annoying, and which bums more fuel than a smooth passage would.  Creating such a smooth passage means adjusting a vehicle's speed so that it always arrives at the lights when they are green.That is theoretically possible, but practically hard.Roadside signs wired to traffic lights can help get the message across a couple hundred metres from a crossing, but such signs are expensive, and are not widespread.Margaret Martonosi and Emmanouil Koukoumidis at Princeton University, and Li-Shiuan Peh at the Massachusetts Institute of Technology, however, have an idea that could make the process cheaper and more effective.Instead of a hardwired network of signs, they propose to use mobile-phone applications. For a driver to benefit, lie must load the team's software , named SignalGuru, into his phone and then put it on a special thing attached to the inside of his car's windscreen, with the camera lens   pointing forward.SignalGuru is designed to detect traffic lights and track their status as red, yellow or green.It broadcasts this information to other phones in the area that are fitted with the same software, and --if there are enough of them ?the phones thus each know the status of most of the lights around town.Using this information, SignalGuru is able to calculate the traffic-light schedule for the area and suggest the speed at which a driver should travel in order  to avoid red lights. Tests in Cambridge, Massachusetts, where five drivers were asked to follow the same route for three hours, and in Singapore, where eight drivers were asked to follow one of two routes for 30 minutes, revealed that SignalGuru was capable of predicting traffic-light activity with an accuracy of 98.2% and 96.3% respectively, in the two cities.This was particularly impressive because in Cambridge the lights shifted, roughly half-way through the test, from their unbusy schedule to their afternoon-traffic schedule, while in Singapore lights are adaptive, using detectors fixed under the road to determine how much traffic is present and thus when a signal  should change.In neither case was SignalGuru fooled. Fuel consumption fell, too --by about 20% .SignalGuru thus reduces both annoyance and  fuel use, and makes going back and forth to work a slightly less horrible experience. SignalGuru is an application used on   _  .
a camera a computer a mobile phone a GPS system in one's car