A Comparison of Daytime and Nighttime Operating Speed on Rural Multi- Lane Highway Sections in Egypt

Traditionally, the 85 th percentile of observed speeds is used to represent the operating speed associated with a specific site with certain geometric features. The presence of sunlight enhances the vision of drivers during daytime while visibility usually degrades during nighttime, especially on rural roads where no street lighting exists, and drivers would depend solely on their vehicle headlights. Visibility degradation is a safety concern which is magnified on horizontal curves. The objective of this study, therefore, is to compare operating speed in daytime and nighttime conditions on both tangent sections and horizontal curves. The analysis made use of spot speed data collected on horizontal curves of two major rural multilane highway in Egypt. Spot speed data were collected using speed guns during daytime and nighttime. The spot speed data were used to calculate the mean speed, variance of speed, and the 85th percentile speed. Analysis of Variance (ANOVA) was used to compare the speeds in daytime and nighttime. For most cases, it was shown that no significant difference existed in speed for daytime and nighttime. This was mainly attributed to the generous design features of the highway elements (e.g., large radii of horizontal curves, wide lanes, etc.). An attempt was made to develop operating speed models to see which variables impact speed during daytime. The results of operating speed models’ development were deemed inappropriate due to the lack of variability in speeds. © 2022 Published by Faculty of Engineering – Sohag University. DOI: 10.21608/SEJ.2022.135873.1012