American Scientist

Scarlett O'Hara may have fanned frantically in Atlanta's humidity, but today the city is becoming known for a different kind of heat. Out on the city's crowded freeways, drivers are getting steamed even in the dead of winter. Now traffic engineer John Leonard at the Georgia Institute of Technology has found a way to measure the city's "traffic temperature" as it shoots through the roof during rush hour. Leonard has even developed a sort of traffic weather map to show drivers just how hot under the collar they might get if they try to traverse the city during a high-congestion period.

Leonard's real-time model of traffic congestion in Atlanta incorporates actual vehicle speeds from traffic-surveillance systems (which are updated every 5 minutes) as well as estimated speeds based on the functional type of road. This information is plugged into an algorithm that provides a congestion index and a map of travel times based on the congestion in different parts of the city. Each colored band on the maps (left) represents about 10 minutes in travel time from the downtown Georgia Tech campus (yellow dot). As the travel temperature rises from a quiet (top) to a busy (bottom) time of day, travel times in many places double.

Ultimately the congestion index may be broadcast on freeway billboards, radio, television and the Internet. A prototype can be seen at the TrafficWeather Web site: http://traffic.ce.gatech.edu/trafficweather/home.asp.—Michael Szpir