Developing passenger car equivalency factors for heavy vehicles during congestion

The Highway capacity manual (HCM) utilizes passenger car equivalency (PCE) factors to estimate the effect of heavy vehicles on traffic stream behavior under free-flow conditions. However, these factors have been (mistakenly) used by professionals to conduct analyses for all traffic conditions, i.e., free-flow as well as forced-flow conditions. Recent empirical evidence suggests that the PCE factors for free-flow conditions largely underestimate the effect of heavy vehicles after the onset of congestion. The current study aims at developing PCE factors for heavy vehicles on freeways and multilane highways during congestion. The study utilizes empirical data and microscopic traffic simulation to develop a set of PCE factors on level terrain and specific upgrades during congestion. The format of the proposed PCE factors is very similar to that of the HCM PCE factors for free-flow conditions. It is believed that the use of the proposed PCE factors for oversaturated conditions will help to largely improve the estimate of heavy vehicles' effect when congestion is present.