Traffic signal preemption (also called traffic signal prioritisation) is a system that allows the normal operation of traffic lights to be preempted. The most common use of these systems manipulates traffic signals in the path of an emergency vehicle, halting conflicting traffic and allowing the emergency vehicle right-of-way, thereby reducing response times and enhance traffic safety. Signal preemption can also be used on tram, light-rail and bus rapid transit systems, to allow public transportation priority access through intersections, and by railroad systems at crossings to prevent collisions. Implementation Traffic preemption is implemented in a variety of ways. Traffic light activation devices can be installed on road vehicles, integrated with transport network management systems, or operated by remote control from a fixed location, such as a fire station, or by an emergency call dispatcher. Traffic lights are equipped to receive an activation signal which interrupts the normal cycle. Traffic signals not equipped to receive a traffic preemption signal will not recognize an activation, and will continue to operate on the normal cycle. Vehicular devices can be switched on or off as needed, but in the case of emergency vehicles, they are frequently integrated with the vehicle's emergency warning lights. When activated, the traffic preemption device will cause appropriately equipped traffic lights in the path of the vehicle to cycle immediately, granting right-of-way in the desired direction, after allowing programmed time delays for the necessary signal changes and for pedestrian crosswalks to clear. Traffic signal preemption systems integrated with train transportation networks typically extend their control of traffic from the typical crossarms and warning lights to one or more nearby traffic intersections, to prevent excessive road traffic from approaching the crossing, while also obtaining the right-of-way for road traffic to quickly clear the crossing. That also allows buses and vehicles transporting dangerous goods to proceed through the intersection without stopping on the railroad tracks. Fixed-location systems can vary widely, but a typical implementation is for a single traffic signal in front of or near a fire station to stop traffic and allow emergency vehicles to exit the station unimpeded. Alternatively, an entire corridor of traffic signals along a street may be operated from a fixed location, such as to allow fire apparatus to quickly respond through a crowded downtown area, or to allow an ambulance faster access when transporting a critical patient to a hospital in an area with dense traffic. Traffic