Assessment of the design of reverse horizontal curves to accommodate heavy vehicles based on simulation

Current geometric design policies use passenger cars as design vehicles, while truck operational and dynamic characteristics are not included or not addressed consistently. Furthermore, critical geometric design parameters such as horizontal curves radii are determined without consideration of the effect of vertical alignment. The objective of this work is to investigate whether critical road sections such as reverse horizontal curves with spiral curves, can accommodate typical heavy vehicles with safety. The analysis was focused on rural and suburban two-lane roads with undivided pavement that produce the largest accident rates. By means of “road – driver - vehicle” simulation system developed in TruckSim, the vehicle dynamic response to inputs from the immediate environment is analyzed, while same kind of outputs that might be measured with physical tests involving instrumented vehicles are calculated and plotted. Results indicated that horizontal curves minimum radii that are implemented according to several design criteria, can not be used in conjunction with the allowed interval of grades, and that the table of minimum radii must comprehend a limitation for the applicable grade. Otherwise, exclusively speed limits depending on the road geometry or larger radii must be used in order to adequately accommodate heavy vehicles.