What are the white lights mounted on traffic signals? They are part of the OptiCom system, which changes the signals in response to an approaching emergency vehicle. The traffic signals change to give the emergency vehicle a green light, and the other traffic a red stop light. The white lights are to warn drivers that an emergency vehicle is approaching, and to pull over out of the way.
The Opticom name is a trademark of the 3M corporation, and the system is also known as Emergency Vehicle Preemption or EVP.
Fire trucks, ambulances, and other emergency vehicles are equipped with a transmitter that sends a high-frequency signal to a receiver at the traffic signals. The receiver sends a message to the signal control box to give the approaching emergency vehicle a green light. The floodlights light up or flash to warn motorists that emergency vehicles are approaching, and they need to stop.
If you see a white floodlight flashing, or lit, at an intersection, it means that an emergency vehicle (or vehicles) is approaching. Pull safely to the side of the road, without blocking the intersection. Wait for all the emergency vehicles to pass, and the floodlight to go out before proceeding.
If the white light is flashing it means that the emergency vehicle(s) are approaching the intersection from a different direction than you are. If you signal is green, it will soon change to red. Treat a flashing white light as a red light. Pull safely to the side of the road and stop. Unless you are in danger of being hit by the car behind, in which case proceed through the intersection, but be prepared to pull over and stop - the emergency vehicles are approaching from another direction, but may be turning down the street you are on.
If the white light is on but not flashing it means that the emergency vehicle(s) is approaching the intersection on the same street that you are on. The emergency vehicles are either in front of you, or behind you. If the signal is red, it will change to green. Treat it as a red light. Pull safely to the side of the road, stop, and wait until all the emergency vehicles have passed. Unless you are in danger of being hit by the car behind, in which case proceed through the intersection then stop safely as soon as you can
