Flow Rates at Signalized Intersections under Cold Winter Conditions

Based on headway data collected under subfreezing conditions, with ice, snow, or frost present, saturation flow rates at signalized intersections were found to be substantially lower than the rates suggested in the Highway Capacity Manual of 1985. A reduction in flow rates on the order of 20% is proposed. A review of available U.S. and Canadian data indicated similar reductions. It was concluded that such reductions should be taken into account for level of service and capacity for areas where temperatures below freezing are encountered for substantial parts of the year. Even when these conditions are encountered for only a few days a year, it may be beneficial to assess levels of service and capacity, based on reduced saturation flow rates, to better understand the operation of the intersections and mitigate the effects of inclement weather.