DELAY-BASED TRUCK EQUIVALENCIES AT SIGNALIZED INTERSECTIONS: RESULTS AND FIELD DATA

Previous studies used the headway concept to compute passenger car equivalents (PCE) for trucks at intersections. The headway-based methods consider only the excess headway consumed by trucks. They yield a constant PCE that is independent of traffic volume and percentage of trucks. To fully consider the adverse effects of trucks on a traffic stream, a new methodology for computing PCE is introduced. The new PCE (D-PCE) are computed based on the additional delay caused by heavy vehicles. Field data showed that the PCE for single unit trucks and combination trucks were different. The PCE are highly correlated with traffic volume and, to some degree, with percentage of heavy vehicles. The PCE computed from field data varied from 1.07 to 1.47 for single unit trucks, and from 1.19 to 1.81 for combination trucks. Although the PCE of 1.5 recommended in the 1985 HCM seems to be more reasonable than the 2.0 recommended in the 1994 HCM, both overestimate the impact of single unit trucks. For combination trucks, the 1994 HCM overestimates the capacity reduction effects of the trucks in most cases.