Traffic signal preemption system

Abstract From the Canadian patent

When placed into operation by the occupants of an emergency vehicle, a vehicle transmission system having a directional antenna sends out a series of UHF messages spaced apart by varying lengths of time and identifying the emergency vehicle, its priority and its, direction, or indicating that the vehicle is travelling along a pre-planned route. At each signal-controlled intersection, a vehicle detection, identification and, preemption system having an omnidirectional antenna and containing information identifying vehicles authorized to preempt the intersection and their pre-planned directions of travel receives these messages from plural vehicles and determines when and in favor of which …