Effects of Environmental Lighting Conditions on Operating Speeds on Urban Arterials

Driver behavior is certainly influenced by the environmental lighting conditions on roads; in literature, many studies report the reduced night/day accident ratio following improvements to lighting on different types of roads, with the results classified by severity and type of accident. Few studies, however, report the influence of lighting conditions on driver speed. In this work the authors investigate the principal factors which influence driver speed on arterial roads in Turin (Italy). The aim of this study is to analyze, in particular, driver speed under different daylight and nighttime lighting conditions. Six arterial roads were selected for observation and the measurement of speeds and illuminance on the pavement surface. The results show that illuminance, in addition to other factors such as lane position, lane width and the relevant speed limit, should be considered a variable that can influence driver speed. In the paper, a regression equation for the prediction of operating speeds (V85) on urban arterials is presented: from a sensitivity analysis thereof, it has been possible to quantify the effects of the above mentioned variables on operating speed under different environmental lighting conditions.