Researchers at the University of Waterloo (UW) in Ontario, Canada, are investigating how cities could ease congestion and improve safety during snowstorms by tweaking the timing of traffic lights to take real-time road conditions into account.
Traffic signals in modern cities are timed using optimization models that analyze factors including traffic volume and speed to safely get as many vehicles as possible through intersections. However, most timing models presume that environmental conditions are ‘normal’, and do not factor in the delays caused by inclement weather. The UW research team collected data and ran computer simulations to determine that adjusting the signals at intersections in bad weather could reduce delays by up to 20%.
Researchers analyzed hours of video taken at a busy intersection near the UW campus to measure how motorists alter their driving behavior during snowstorms in terms of speed, stopping distance and other variables. That data was then used in computer simulations using Trafficware’s Synchro Studio and PTV’s Vissim software to optimize the timing of signals, including the periods of the green, yellow and red 
intervals, at a single intersection and on a stretch of road with four coordinated intersections. Changes were also made to improve safety, such as increasing the yellow interval to account for vehicles traveling slower and requiring more time to stop on slippery pavement surfaces. At the single intersection, changes to increase safety and reduce delays almost canceled each other out. However, the UW team found that even with the adjustments to help avoid crashes, intersection delays in the coordinated corridor, especially in moderate traffic, decreased by up to 20%.
The project lead, Liping Fu, a civil and environmental engineering professor and director of the Innovative Transportation System Solutions (iTSS) Lab at UW, noted that cities with computerized signal systems are already equipped to remotely and inexpensively adjust the timing of traffic lights to reap those benefits when snowstorms hit. The team’s next steps 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. A research paper, Effects of winter weather on traffic operations and optimization of signalized intersections, authored by Fu and former Waterloo graduate students Zhengyang Lu and Tae J Kwon, is published in the February edition of the Journal of Traffic and Transportation Engineering.
“The problem with standard signal timings is that their parameters all assume normal weather conditions,” explained Fu. “In the winter, if the road surface is covered with snow and ice and visibility is poor, the numbers are not the same. We need to have weather-responsive signal plans. Their timing should recognize weather conditions and change accordingly. 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.”
