Night-time and daytime operating speed distribution in urban arterials

- Effects of lighting conditions on operating speeds on urban arterials are explored.
- Random effects model to estimate the entire speed distribution along road sections.
- Average speeds and deviations increase when illuminance increases.
- At night-time, the considerable variation in speed due to driver behaviour.
- Random effects often appear to be very low and sometimes negligible.

Operating speeds on roads are influenced by lighting conditions: indeed most of the driving tasks are influenced by visual information. In terms of supporting evidence, there is a significant volume of published research that demonstrates how safety is affected by road geometrics and environmental lighting conditions. However, only a few studies have investigated the contextual impact of these factors on driver speed behaviour, which in turn is considered one of the most important variables affecting road safety.In this paper, speed distributions have been modelled using environmental parameters related to both road geometrics and lighting conditions. To achieve this, the authors compiled a comprehensive database in which geometric characteristics, speeds, illuminance and luminance are available for both night-time and daytime conditions. The results show that average speeds and deviations from the mean are significantly affected by changes in lighting parameters for the different conditions (sunny, cloudy, and dark) considered in this study. Knowing the effects of such parameters on operating speed is fundamental for effective road management policies, especially on urban roads where, notably, the highest number of accidents occur.