Analyses of Vehicle Trajectories and Speed Profiles Along Horizontal Curves

Vehicle speed and lane position are two of the many possible factors that lead to crashes on horizontal curves. Vehicle position and speed through horizontal curves are of great relevance to many areas of traffic engineering, including countermeasure design, design consistency, and policy. This article discusses the results of an exploratory analysis of vehicle trajectories and speed profiles at two horizontal curves located in central Iowa. The sites include an urban and rural curve. Data were collected at five stations within the horizontal curves in both directions of travel using pneumatic road tubes set up in a Z-configuration. Overall, vehicles were found to cut the horizontal curve in the inside and outside travel lanes. However, the trajectories were seen to be different at the two curve sites. Vehicle mean speed profiles indicated that the curve site selected for evaluation operate differently and are reflected in the speed profiles. Speed deviations of individual vehicles as they traversed the curve were evaluated. More vehicles were found to adjust their speeds and lateral position in the vicinity of the center of the curve, and then at the end of the horizontal curve.