Why Your Car May Have Trouble Running Traffic Lights in Snow

There was a time when most robots worked by relying on timers. This is wrong as anyone sitting at a bus stop in the middle of the night with no other cars on the road can testify. Today, many signals use sensors – such as inductive loops – to detect the presence of vehicles and adjust the lights accordingly.

Inductive loop sensors use a coil of wire, usually embedded in the road near a stop sign. When the car rolls through that loop, the metal in the car disrupts the magnetic field in the coil, signaling the traffic controller that someone is waiting. These programs are not dependent on weight, as is commonly believed. Instead, they rely on the presence of bars in the car, which is why motorcycles and bicycles can sometimes be difficult to open if they are not parked correctly.

So, why does your car seem to have trouble turning on the lights in the snow? Of course ice cannot block the magnetic signal. After all, magnets work well under water, so a little ice shouldn’t leave you stuck to the stopper. Thankfully, though, these robots don’t break the laws of physics, which would be weird and very important news. The truth seems to be very simple. Snow obscures road signs that tell drivers where to stop. Sit too far back, a little in the middle, or too far forward, and you won’t miss the most sensitive part of the zone entirely.

A 2019 paper published in ScienceDirect suggests that inclement weather — including snow, ice, and fog — contributes to about 544 million vehicle delays each year in the US, accounting for about 23% of all non-recurring highway delays. While it’s a stretch to suggest that all of these delays can be caused by traffic lights failing to see waiting cars, the cumulative effects of any traffic light-related problems could add to the frustrations of drivers. Yes, some lights – like the most annoying traffic light in US history – manage this in any weather, but snow can make it worse.

That’s why the advice from Jason Saliba, a robotics engineer, is worth paying attention to. Speaking to KY3 News, Saliba explained that the snowy condition itself is not common and is the reason why the robots fail to respond. Rather, and as noted above, the problem can be as simple as where the driver parked his car.

The solution is straightforward. As Saliba explains, “If you don’t think your car is being detected, you can try to reposition yourself closer to the center of the lane.” He also suggested that you need to get closer to the stop bar, noting that they are usually “about 10 feet behind the curb of the crosswalk.”