Energy efficient traffic lights could pose a problem in cold, snowy Canadian cities.

New LED bulbs don't generate the same amount of heat the old incandescent bulbs did, so they don't melt the snow that builds up on traffic lights.

Thursday in Windsor, Ont., police say a school bus ran a red light and broad-sided a car in an intersection. Six kids, a school staff member, and the drivers of the car and bus were taken to hospital. Police said the bus driver claimed the red light was covered in snow.

John Wolf, senior manager for traffic operations at the City of Windsor, said city officials have been unable to come up with a workable solution to the snow build-up.

"LEDs do not put off any heat. The old heads were just 150 watt, so basically [stoplights] had a 150-watt light bulb in them, so they generated heat and anything on them melted," Wolf explained.

Wolf said for the time being, when snow builds up on a traffic light, city work crews have to clean the lights off by hand, and that takes a lot of time.

The City of Windsor is converting all traffic signals over to LED technology as the old bulbs fail or signals need upgrading.

The LED traffic lights cost more, but use one quarter the energy of incandescent bulbs, so they save the city money over time.

There are also savings on maintenance. Incandescent bulbs have to be replaced every two or three years. LEDs are supposed to last at least twice as long.

The City of Windsor isn't the first Canadian city to experience snowy stoplights. Charlottetown encountered the problem back in 2013.

Charlottetown public works manager Paul Johnston told CBC at that time crews had to go out and fix the problem of snow-covered traffic lights during a storm.

"The staff have gone out and just tried to vibrate the poles slightly, and that, in some cases, has been enough," Johnston said at the time..