Explanation of Traffic Signal Preemption

The normal operation of any traffic signal controlled intersection is designed for the maximum and efficient throughput of vehicular traffic.

Unfortunately, a common occurrence at any intersection is traffic back-up, which can require many signaling cycles to clear. Without the ability to change the operation of the traffic signals themselves, police and emergency response vehicles can also be forced to sit in traffic, thus dramatically increasing their response times to crime scenes and fire or medical emergencies.

Furthermore, even without heavy traffic, a police or emergency response vehicle entering a traffic signal controlled intersection at a high rate of speed places all motorists (and sometimes pedestrians) at extreme risk.

Traffic signal preemption is an optical communications system that allows preemption-equipped vehicles to alter the normal operation of preemption-equipped traffic signals.

An overview of a typical scenario is as follows:

A fire truck is dispatched to an emergency.

The fire truck is equipped with multiple emergency warning lights and a siren… The fire truck is also equipped with a preemption transmitter, which, in operation, is a high intensity forward-facing strobe light that is flashing at a rapid rate - much faster than normal attention-getting lights on the fire truck.

When the fire truck approaches within 1,800 feet (line-of-sight) of a preemption-equipped traffic signal controlled intersection, the preemption detector (normally mounted on the cross-arm that suspends the traffic signal) "sees" the fire truck’s preemption transmitter and locks onto its flashing strobe.

Once the traffic signal "sees" the fire truck, it begins to initiate a "preemption sequence" of the actual traffic signal that is different from normal operation.

If the fire truck already has a green light, the light will remain green. Any other direction that also has a green light (usually the opposite direction) will first get a yellow light, then red.

When all of the other directions are then red, and the fire truck’s direction is the only one that is green, the left turn arrow will illuminate (if one exists), and a brilliant white flood lamp mounted near the traffic signal will begin to flash. This flood lamp tells the driver of the fire truck that he now has control of the intersection, and complete right-of-way.

If the fire truck has a red light, any other direction that has a green light will transition to yellow, then red. When all the directions (including the fire truck’s) are red, the traffic signal facing the fire truck will then turn green, along with the left turn arrow (if one exists), and the brilliant white flood lamp will begin to flash.

Once the fire truck has passed through the intersection, optical communication with the preemption detector (on the traffic signal) is lost. At that time the traffic signal will default back to normal operation. Conversely, until the fire truck passes through the intersection, it will have a green light, regardless of the time duration.

If several intersections are within the 1,800 foot range of the fire truck’s preemption transmitter, they will all respond accordingly to the above operational description.

TERMS OF AGREEMENT FOR PURCHASE OF THIS DEVICE:

Purpose: The purpose of this document is to establish the party named below as an authorized end-user of the product called The MIRT. The MIRT traffic signal preemption emitter is a restricted sale device. By agreeing to this document the part named above agrees to all information contained herein. It is the express purpose of MyAA.us to prohibit the use of traffic signal preemption products by unauthorized individuals by restricting the sale of such devices to those departments and individuals that are legally entitled to use them. See your state's Department of Transportation’s web site to learn more about your state’s regulation of these devices.

1. Traffic signal preemption products purchased will be used in accordance with governing state and local laws, and only for official department business and/or emergencies.

2. Traffic signal preemption products purchased will only be used by authorized personnel, and only for the purpose stated in item “1” above. “Authorized Personnel” are only those individuals who are legally entitled to preempt traffic signals in accordance with governing state and local laws.

YOU MUST AGREE TO THESE TERMS TO PURCHASE THIS ITEM