||Driver behavior is influenced by environmental lighting conditions on roads; in the literature, many studies report a 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. This study investigates the principal factors that influence driver speed on arterial roads in Turin, Italy. The aim of this study was to analyze 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 showed that illuminance, in addition to factors such as lane position, lane width, and the relevant speed limit, should be considered a variable that can influence driver speed. The study used a regression equation to predict operating speeds (V85) on urban arterials; the corresponding sensitivity analysis has made it possible to quantify the effects of the aforementioned variables on operating speed under different environmental lighting conditions.