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The Eden Prairie Police Department blog provides an opportunity for the public to learn more about the people who work there — their stories, their lives, their work in Eden Prairie and their thoughts on topics from driving to dogs.

Those Flashing Things on Stoplights

Post Date:June 11, 2019 11:40 AM

traffic signal with opticom

Have you ever been driving around town and noticed a flashing white light on top of a stoplight? Have you ever wondered about its purpose and how it works? Well here is your answer. Those lights are called pre-emption devices and their purpose is to control traffic while an emergency vehicle responding to an emergency call makes its way safely through an intersection with a stoplight.

Here’s how it works: inside each emergency vehicle is an emitter which controls the vehicle’s lights and sirens. The driver of the vehicle can select one of three levels while travelling to an emergency call. One of the levels, called Code 3, sends a signal to the pre-emption device on top of a stoplight in order to change the signal so the vehicle can pass through safely. At the same time, the pre-emption device stops traffic coming from the opposite direction from entering the intersection.

If the light on the pre-emption device facing you is flashing or solid white, that means an emergency vehicle is approaching the intersection. In that case, you should pay attention to traffic in all directions and be prepared to move your vehicle to the side of the road.

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