(WHTM/NEXSTAR) – On many traffic signals found throughout the United States, there is a small light that is placed in between or off to the side of the traffic signal lights. Sometimes you see them blink when emergency vehicles are passing through.

So, what are they?

These are called priority or preemption signals. The lights are part of a system that allows the operator of a vehicle to override the normal operation of a traffic light.

Maricopa County, Arizona, Emergency Vehicle Preemption (EVP) systems were first installed in the early 1980s in hopes that they would reduce response times. Fire engines and other emergency vehicles are equipped with emitters that communicate with receiving devices on traffic signals.

When an emitter is activated, the device will cause the traffic lights in the path of the vehicle to immediately cycle and grant the right of way in the direction the vehicle is traveling.

These preemptive indicators allow emergency vehicles to get to scenes faster and clear a path for the vehicle. It can also improve safety by giving a red light to all other lights at the intersection, so no traffic impedes an emergency vehicle.

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Many preemptive indicators have confirmation lights installed on them. That is the white light people see when they are activated. The light can be blinking or solid, both of which have different meanings.

In Pennsylvania, for instance if the light is steady that means that the signal has been preempted and will give a green light for a signal in that direction. However, if the light is flashing, it means that the signal has been preempted to give the green light in a different direction.

Some of these systems use a line of sight system, which allows for a narrow signal directed forward toward traffic lights in front of the vehicle to get the right of way. Others use GPS and some use a radio signal to get the same right of way.

South Georgia Medical Center, which announced in June, 2023 that it would equip all of it’s ambulances with GPS-ready EVP devices to help responders stop cross traffic as they rush to an emergency.

“This innovative technology makes ambulance responses safer for everyone,” South Georgia Medical Center EMS Chief Michael Colman said in a statement.

The hospital group found that the devices have reduced response time by an average of 11 seconds per traffic light.

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