Emergency Vehicle Preemption
Emergency vehicle preemption (EVP) is designed to give emergency response vehicles a green light on their approach to a signalized intersection while providing a red light to conflicting approaches. The most commonly reported benefits of using emergency vehicle preemption include improved response time, improved safety, and cost savings.
When preempting coordinated traffic signals, EVP removes the preempted signal from the coordinated system, so that the signal can respond to the emergency vehicles preemption call and give the approaching emergency vehicle a green light. A green light gets the queue moving and the traffic dispersed before the emergency vehicle arrival allowing the emergency vehicle to maintain higher average speeds than would be expected given intersection spacing along the route and normal traffic conditions. Emergency vehicle preemption can reduce the chance of an emergency vehicle crash at a signalized intersection. Improved response times can lead to an improvement in the insurance industry ratings of a community's fire suppression service.
Some communities install confirmation lights in conjunction with the detectors. This light provides feedback to the emergency vehicle driver that the request for preemption has been received and that the request will be served according to the local preemption transition protocol.
Confirmation lights are intended to communicate to approaching emergency vehicle drivers the status of the traffic signal. There are three stages of operation for the lights:
- Stage 1, normal status is, when the light is dark. The confirmation beacon will be in this state the majority of the time and the system is considered to be in the listening mode.
- Stage 2, a solid white light on, communicates to approaching emergency vehicles that the traffic signal preemption system has received their infrared signal and it is processing in their call. The time to process the vehicle preemption call varies depending upon the phasing (i.e. turning, and through movements) that the traffic signal is serving at the time when the preemption call is received.
- Stage 3, a flashing white light, communicates to approaching emergency vehicle drivers that the traffic signal is currently processing an emergency vehicle preemption call on one of the other approaches to the intersection and, therefore, their call will not be processed until the other call has expired (the other emergency vehicle went through the intersection)..