Researchers at Waterloo Engineering have determined how to adjust the timing of traffic lights to reduce delays and improve safety during snowstorms.

Waterloo Engineering researchers have found an inexpensive way for cities to ease congestion and improve safety by tweaking the timing of traffic lights during snowstorms.

After collecting data and running sophisticated computer simulations, the researchers found that adjusting signals at intersections to take poor road conditions into account could reduce delays by up to 20 per cent.

“We need to have weather-responsive signal plans,” says Liping Fu, a civil and environmental engineering professor. “Their timing should recognize weather conditions and change accordingly.”

Civil and environmental engineering professor Liping Fu.

Civil and environmental engineering professor Liping Fu.

Signals in modern cities are timed using optimization models that analyze factors including traffic volume and speed to get as many vehicles as possible safely through intersections.

“The problem is that those parameters all assume normal weather conditions,” says Fu, director of the Innovative Transportation System Solutions (iTSS) Lab. “In the winter, if the road surface is covered with snow and ice and visibility is poor, the numbers are not the same.”

Researchers analyzed hours of video taken at a busy intersection near campus to measure how motorists alter their driving during snowstorms in terms of speed, stopping distance and other variables.

That data was then used in computer simulations to optimize the timing of signals – the green, yellow and red intervals, for instance – at a single intersection and on a stretch of road with four co-ordinated intersections.

Changes were also made to improve safety, such as increasing the yellow interval to account for vehicles travelling slower and requiring more time to stop.

At the single intersection, changes to increase safety and reduce delays almost cancelled each other out.

But even with adjustments to help avoid crashes, intersection delays in the co-ordinated corridor, especially in moderate traffic, decreased by up to 20 per cent.

Cities already equipped to tweak timing of traffic lights

Cities with computerized signal systems, Fu says, are already equipped to remotely and inexpensively adjust the timing of traffic lights to reap those benefits when snowstorms hit.

Next steps for the researchers include the development of technology using video cameras and artificial intelligence (AI) software to automatically tweak the timing of lights in response to traffic changes caused by weather, accidents or construction.

“Ultimately we want signal controls so smart that they actually change themselves in real time based on what is happening in the road network for any reason,” Fu says.

A research paper by Fu and former Waterloo graduate students Zhengyang Lu and Tae J. Kwon, Effects of winter weather on traffic operations and optimization of signalized intersections, is to appear in the Journal of Traffic and Transportation Engineering.