If you're driving around Minneapolis/St. Paul, you might be wondering what the white lights mounted on traffic signals are. They are important and might save lives. These lights 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 that they should 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. Minneapolis/St. Paul is just one city that uses the system.
How the Lights Work
Firetrucks, 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 pull over and/or stop immediately.
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 but do not block the intersection. Wait for all the emergency vehicles to pass and the floodlight to go out before you start driving again.
Flashing White Lights
If the white light is flashing it means that emergency vehicles are approaching the intersection from a different direction than you are. If your traffic 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. If you are in danger of being hit by the car behind you, drive through the intersection but be prepared to pull over and stop; the emergency vehicles are approaching from another direction, but they might be turning down the street you are on.
Non-Flashing White Lights
If the white light is on but not flashing it means that emergency vehicles are 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. As with flashing lights, if you are in danger of being hit by the car behind you, go through the intersection then stop safely as soon as you can.
The Urban Legend
According to the Gallax, Virginia's (a town using Opticom) Fire and Rescue website, there is an urban legend claiming the system can be tricked by a car flashing their high beams. They counter that urban legend by pointing out that the system cannot be spoofed by flashing high beams since it is activated by a visible light and/or invisible infrared signal, operating at a specific “flash-rate” frequency. They indicated that typical activation settings for an Opticom system are around 600 or 900 FPM (flashes per minute), or 10 to 15 “flashes” per second, which is not something you can do with your high beams.