The Fantasy of Changing Traffic Lights to Green is Real, But You Might Have to Do Some Time

Emergency and mass transport vehicles are equipped with devices that turn traffic lights green, if you have a yen to do the same, you could be in big trouble.
Marcia Wendorf

You're sitting at a red traffic light wishing it and all its brethren in front of you would turn green. It turns out that during the wild and woolly aughts, you could actually make this happen.

The process is called traffic signal preemption, and it's been around for over 20 years. Emergency vehicles have used it as a way to get to incidents quickly by halting conflicting traffic and giving themselves the right of way.


Traffic signal preemption is also used by light rail and bus rapid transit systems, and by railroad systems at level crossings. The system is used near fire stations to change traffic lights in order to allow emergency vehicles to exit the station.

Opticom receiver and notifier in Millersville, Pennsylvania
Opticom receiver and notifier in Millersville, Pennsylvania, Source: Niagara/Wikimedia Commons

How it works

Traffic lights must be equipped with a receiver, and a vehicle, bus, train or fixed building must be equipped with an emitter that produces either visible flashes of light or invisible infrared pulses at a specified frequency.

Infrared pulses are created by a Mobile Infrared Transmitter (MIRT) that consists of a timer circuit and an infrared LED array. The infrared LEDs can strobe at 10 Hz for low priority vehicles, such as buses, or at 14 Hz for high priority vehicles, such as fire trucks. They will work from up to 1,500 feet away from a traffic light.

In the U.S., two major companies, 3M and Tomar Electronics Inc., sell traffic signal preemption devices. Some traffic signal preemption systems include feedback for both emergency vehicles and other drivers that a traffic signal is under the control of a preemption device.

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Called a "confirmation beacon", it is an additional light located near the traffic signal that either flash to tell drivers to stop, or stays on to tell drivers from what direction the emergency vehicle is coming.

Newer traffic signal preemption systems include a security feature that requires a serial number to accompany the emitter's signal. These newer systems also keep track of every time a traffic signal is activated, so with the addition of a traffic camera, finding unauthorized users isn't hard.

If you aren't afraid of prison

In the mid-2000s, you could buy MIRTs openly on eBay, then in August 2005, the Safe, Accountable, Flexible, Efficient Transportation Equity Act was passed. It set a minimum sentence of six months in prison for anyone using the devices, and a year in prison for anyone selling the devices.

Surprisingly, we found that you could still buy traffic signal preemption devices online, and we found the internet to be awash in videos showing how to create one of the devices yourself.

Youtube user VolteGe, who says he is too young to drive, has nevertheless created a MIRT controlled by an Arduino microcontroller.

And, according to Youtube user frost5000000, you can change traffic lights to green just by using your cellphone.

User Dane Boe shows how to create an emitter using a TV universal remote control.

According to website, a Longmont, Colorado man was fined $50 when police identified his white Ford pickup at the site of numerous traffic preemptions. Commenting on the site, a traffic engineer said that the use of signal preemption equipment was very common in Northwest states such as Oregon where receivers are installed at 80% of intersections.

Finally, it is an urban legend that you can strobe your car's high beam lights to activate traffic light preemption. You would need to flash them at a rate of 10 to 15 flashes per second which would be difficult at best.

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