Good Question: What Causes Traffic Lights To Go Out?

MINNEAPOLIS (WCCO) -- It's one of those inconveniences in life that always comes at the worst time. You're in traffic and all of the sudden the light goes out, leaving you and your fellow drivers to wonder what happened.

For three days this week, Minneapolis drivers had to put on the brakes at 2nd Avenue and 11th Street downtown. The signal went out Monday night and didn't get fixed until Thursday.

"People aren't happy. Especially when it goes into the day format, when it's not just hours, it's days," Steve Mosing said.

Mosing is the traffic operations engineer for the City of Minneapolis, and he's in charge of making sure the city's 806 traffic signals are running smoothly.

"Sometimes you have a power outage that will be really brief and quick and for that reason the system will go to a flash for a safety precaution," Mosing said.

Along with a power surge, rainy weather can cause moisture build-up inside the cabinet where the signal controller is stored, causing the lights to go into flash mode.

But the reason the signals were out at 2nd Avenue and 11th Street is one of the most common reasons traffic signals go out.

"Usually a car has hit it," Mosing said.

That's what happened in this case. If a car hits the cabinet hard enough the wiring and everything inside needs to be rebuilt before the signals can come back on. Each controller is different, according to Mosing.

"What we do is when we rebuild the controller. We test it for a day or two to make sure it's going to operate correctly in the field before we install it," Mosing said.

It generally takes up to 48 hours to test a rebuilt signal controller before it can begin working. But it's not just time for drivers; it's money, too. The driver in a crash is responsible for paying the damage and it's never cheap.

"The controller, which is again the intelligence at the intersection, can cost up to $50,000 to $60,000 sometimes," Mosing said.