Horizontal Curves,Signs,and Safety

Although the safety of horizontal curves has been researched, data availability and quality have been the Achilles' heel of many studies. Furthermore, safety at horizontal curves has become more significant in view of the changes in the latest Manual on Uniform Traffic Control Devices with respect to traffic control devices at horizontal curves. The objective of this research was to evaluate the safety of horizontal curves through the use of curve geometric characteristics and sign data. The focus was on collecting a good-quality large data set to develop models and explore the relationship between safety at horizontal curves and sign types, specifically curve and turn signs. The data set included curves on different types of roads to determine the difference in safety characteristics that had not been examined in the literature. The crash prediction models displayed highly significant variables, which showed a positive relationship with annual average daily traffic, posted speed, and curve length, and a negative relationship with curve radius. The results show that sharper curves (Classes B–F) on two-lane roads are less safe than curves on freeways and multilane and urban roads. However, further investigation is required into the safety characteristics of Class A curves on freeways and multilane roads, compared with two-lane roads. Moreover, sign usage was not found to be a significant factor for sharper curves, which suggests that, regardless of the presence of the curve or turn sign, other influencing factors take over. The crash prediction model results provided greater detail and identified variables with large significance.