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GLAD YOU ASKED: Traffic light changes at intersections depend on location of vehicle

Sensors placed into the pavement shown in this picture are placed in the street along street lights to switch the lights. (Jordan Steffen/Daily Republic)

Q: I'm a motorcyclist and I'm wondering why traffic lights won't turn green for us bikers. Particularly troublesome traffic lights are located along Sanborn, at the intersection of Minnesota and Havens, and at the intersection of Spruce and Burr. I'm sure other bikers have seen this at other intersections. Many times I have sat at these intersections for minutes at a time with no change, whether there is traffic running or not, and have had no choice but to run a red light after waiting for a green light to no avail. As soon as a car or truck pulls up, however, it seems to change. What gives and what can be done about it?

A: When and if traffic lights change depends on the location of a vehicle, said Dick Figland, traffic specialist for the city of Mitchell. "Some signals have a vehicle detection system on the street," he said. "If you're not pulled up to the right place at the stoplight, the light's not going to change. You could be too far back, or you could be too far forward."

Most traffic light intersections in Mitchell contain a vehicle detection system, which consists of two to three 4-inch by 4-inch squares placed in the pavement, typically beneath the white bar painted just before a traffic light. Those squares create a loop that, when interrupted by a vehicle, triggers the controller in the traffic light to change the signal, Figland said. If a light isn't changing, it could be one of two things -- there could be a mechanical failure or the vehicle didn't stop in the right place and didn't trigger the loop.

His advice for bikers:

"Ninety percent of the time there's going to be a loop where the stop bar is painted," Figland said. "Stay in the center of the lane and pull on top of the stop bar, the white strip just before the crosswalk."