Heavy vehicles have a considerable effect on traffic capacity, despite contributing only a relatively small proportion of total traffic volume. The effect is most significant in areas comprising steep grades, intersections, and congestion. Current capacity prediction models estimate the impact of heavy vehicle traffic using equivalent passenger car units (PCU) to represent a heavy vehicle. The PCUs vary according to vehicle type, local topography and traffic flow conditions. Some researchers have indicated that current PCUs are out-of-date or not representative of the modern Australian heavy vehicle fleet. To address this, a review of PCUs was undertaken, with new factors developed using microsimulation for rural (using TRARR) and urban (using VISSIM) scenarios. The simulations were calibrated to match the performance characteristics of modern vehicles using ARRB heavy vehicle simulations. The resulting PCUs varied considerably with variables including vehicle type, grade and grade length. Comparing currently used and developed PCUs shows similarity for semi-trailers, but differences for previously untested large vehicles (such as B-triples), and were significantly higher on long and steep upgrades. It is considered that PCUs, particularly in urban situations, are sensitive to many parameters and must be used with due consideration of the case for which they were devised. (a) For the covering entry of this conference, please see ITRD abstract no. E217099.
Samenvatting