Passenger car equivalent factors for level freeway segments operating under moderate and congested conditions

The significant impact Heavy Vehicles (HV) have on freeway operations has been identified since the first edition of the Highway Capacity Manual (HCM). The method of incorporating their impact in freeway capacity calculations has changed through the years. The HCM 2000 used Passenger Car Equivalent (PCE) values and percent of trucks/buses and Recreational Vehicles (RV) to account for HV effect on capacity. However PCE values in the most recent HCM edition rely on a limited field database and extensive simulation runs based on this information they were calibrated on 'steady-flow' traffic operations. The objective of this effort was to indentify and quantify HV characteristics that have an impact of freeway throughput at various congestion levels on level, urban freeways using 1.2 million individual vehicle observations, with an emphasis on operations at LOS E and F. It was desired to use the products of this effort as recommended inputs for future simulation runs of congested freeway flow conditions. Passenger Car (PC) and HV headways were found to increase with HV presence in the traffic stream. A similar pattern was found for the PCE factor. The PCE value, under congested conditions and more than 9% HV presence, was found to be 1.76, which is higher than the HCM 2000-recommended value of 1.5 for level freeway sections. Also, passenger car was found to have the effect of more than 1 PC at congested condition with high HV presence.