Watching the Big Wheelers: In sea of cars, trucks reveal traffic flow

Traffic managers in urban settings monitor networks of roadway sensors as one way to detect congestion. The faster those networks recognize problems, the quicker authorities can alert motorists and emergency teams to possible trouble.

IN THE LOOP. A fast, new way to automatically detect traffic congestion relies on distinctive electric signals generated when trucks and other long vehicles pass over wire-loop sensors under the roadway.