Developing Passenger-Car Equivalents for Heavy Vehicles in Entry Flow at Roundabouts

Abstract

This study develops passenger-car equivalents (PCEs) for heavy vehicles at roundabouts. For this task, the movements of cars and heavy vehicles were observed using video records collected from three roundabouts in Vermont; Ontario, Canada; and Wisconsin. The PCE was developed such that the variation in the entry capacity in a various mix of cars and heavy vehicles was minimized. The PCE was also applied to the prediction of the entry capacity using a roundabout capacity model. For the model inputs, the study adjusted the critical headway and the follow-up headway to account for the difference in driver’s gap acceptance behavior between cars and heavy vehicles. The result shows that the PCEs for heavy trucks and light trucks are 1.5–2.5 and 1.0–1.5, respectively, at the three roundabouts. In particular, the PCE for light trucks was lower than a default value of 2.0. The result also shows that the established model generally predicted the capacity more accurately when the critical headway and the follow-up headway were adjusted by different weights instead of the same weight (i.e., the default value of the PCE).