The need for nighttime design consistency evaluation: an exploratory study

Crash data in the USA show that approximately 47 percent of fatal crashes occur at night. Sight distance is severely reduced at nighttime as it compares to that in the day often resulting in problematic situations. Horizontal alignment can compound this issue, since most drivers would not be able to see far in advance to recognize the sharpness of the curve and adjust their speed accordingly: a process that they can complete at daylight conditions. This study attempts to understand the influence of roadway geometry and especially curvature on nighttime crashes and presents a preliminary analysis of this issue aiming to identify the magnitude of the problem and provide some guidance for future research. The findings indicate that there is indeed an increased crash occurrence at night and this is related to the curve radius. Sharper curves, i.e., curves with small radii, showed an increase in crashes and crash rate when they were compared to their corresponding daytime crashes. Design consistency was also examined by considering the radii of successive curves. The data again points to the differences in crash experience when considering the relation between two successive curves. Additional work is needed to further explore these issues and develop more statistically robust models for refining the nomographs developed here.