Nighttime versus Daytime Horizontal Curve Design Consistency: Issues and Concerns

Abstract

Approximately 47% of fatal crashes in the US and 36% in the European Union occur during the night. Reduced sight distance may contribute to this phenomenon and similar speeds driven between day and night can become problematic along horizontal curves. In this case, drivers are not provided adequate time to adjust their speed for safe negotiation of the curve which can be completed under daylight conditions. This study is the first step toward demonstrating the influence of curvature on nighttime crashes through a preliminary analysis aiming to identify the magnitude of the problem. Data from the US and Greece have been examined and the findings indicate that there is indeed an increased crash occurrence during the night related to the curve radius. Curves with small radii showed an increase in crash occurrence and rate compared to that of corresponding daytime data. The radii of successive curves were utilized as a measure of design consistency and the data again noted differences in crashes between daytime and nighttime conditions.