Determination of Passenger Car Equivalent for Heavy Vehicles in Iran in Comparison with Highway Capacity Manual 2016

Two-way two-lane (TWTL) carriageway comprises a considerable portion of the road network in developing countries. Thus, reliable road capacity estimation is of great importance for road design, operation, and planning. Furthermore, heavy vehicles’ presence causes an extreme variation in roads’ operation and level of service, especially on different slopes. This paper investigates the effects of heavy vehicles in the traffic stream by using the concept of passenger car equivalent (PCE) from Highway Capacity Manual 2016 (HCM2016) and then calibrates it for developing countries such as Iran. This research aims to determine PCE factors for heavy vehicles in Iran’s TWTL roads with diverse geometrical and traffic conditions. Accordingly, PCEs were calculated by two approaches, and the results were compared with HCM factors. The conclusion indicates that by increasing the TWTL road slope, PCE factors increase, but when the traffic volume increases, PCE factors decrease. However, the extent of PCE increase or decrease was not always equal to the correspondent values specified in HCM2016. It was observed that as the length and the slope increase, the PCE values reported by HCM have a higher rate than the ones estimated for Iran. For 5.5–6.5% slopes, the HCM PCE factors were almost twice Iran’s calculated ones.