More than 2,000 trucks a day encounter the weigh station on Interstate 55 near Williamsville. With PrePass, more than 300 are allowed to pass without stopping.
A weigh-in-motion scale in the road lets officials know whether the trucks are overweight. A transponder attached to the windshield transmits tax and safety information. If the truck checks out, a green light shows on the transponder, and the driver can continue. A red light means pull over.
About 70,000 trucks licensed to operate in Illinois have PrePass transponders.