(NEXSTAR) – It’s probably happened to you. You pull up to a stop light, and you wait patiently for the light to turn green. Maybe cross traffic continues moving through the intersection, or maybe you’re the only car at the intersection.
Yet somehow, the light never seems to turn green.
Chances are, you’re sitting at a light that doesn’t know you’re there.
Some traffic lights run on timers, which can vary by the time of day or during certain events. In Minneapolis, for example, there are set patterns for lights during Minnesota Twins or Timberwolves games and other special events.
If that’s the case, you’ll be stuck waiting your turn for the light to change.
However, other traffic lights rely on detection devices, including cameras or underground sensors.
You’ve likely seen the latter — before the stop line, you’ll notice a rectangle outlined in tar or that has a different color than the pavement around it. This is known as an induction loop.
“A loop is simply a coil of wire that is placed underneath the pavement, usually in the shape of a rectangle,” the public works department for Neenah, Wisconsin, explains. “When a large metal object is positioned over the loop (for example, a car), it affects the loop’s magnetic field.”
Once the traffic signal detects your vehicle, it knows it has to change the light.
Sometimes setting off these sensors can be difficult since vehicles need to pass over or stop within its detection area. To ensure you’re within that detection area, you’ll need to pull up to the solid white stop line at the intersection.
Not driving a car? Instead of parking your motorcycle, bicycle, moped, or other similar vehicle in the center of the loop, Neenah Public Works recommends positioning your tires on the tar lines.
Two other sensors, magnetic detectors and magnetometers, detect differences in the Earth’s magnetic field, caused by a vehicle passing over or stopping on it, to control the lights, according to the U.S. Department of Transportation Federal Highway Administration. Like the induction loop, you’ll need to position your vehicle over the detectors to activate the light.
A traffic signal may also rely on sensors stationed above the roadway.
That includes infrared sensors, which are triggered once a vehicle breaks a beam of light or if it detects heat from a vehicle’s engine. Other signals may also use cameras, which can be connected to a network designed to detect traffic and adjust the signals as needed (those cameras may also be watching to catch drivers that run red lights).
You should be able to see both at the traffic light. They’ll look like a security camera you may see at a bank or store, often next to the traffic light itself. Some infrared laser sensors are contained in metal boxes hanging above the roadway.
In many cases, an intersection will rely on a combination of the above methods to control the lights. Los Angeles, for example, deployed a system in 2021 that uses magnetic sensors, cameras, and a central computer network to control all of its 4,400 traffic lights to combat gridlock.
If you are stuck at a red light, and have already tried pulling forward onto the sensor, you can also try flashing your high-beam headlights to activate the sensor. Honking your horn will not work, since these sensors don’t detect sound.
Even if it’s taking a long time to change, don’t run it. If you’re trying to turn left or go straight, you may need to look for another opportunity to get out of the intersection.
This could include making a right turn, where legal, and rerouting yourself where you need to go. If you find yourself waiting on a left turn light, you can turn through the red signal when the light turns green for traffic traveling straight ahead, California Highway Patrol Officer Dan Olivas explained to the Press Enterprise.
He encourages being “safe about it” and, if you are stopped, explaining the situation to law enforcement.
