Determination and Evaluation of Passenger Car Equivalent for Two-Lane Two-Way Highways of Iran Based on Speed-Difference and Headway Methods

Two lane two-way highways comprise major portion of national highway network. They provide the possibility of overtaking in opposite direction of flow. The capacity of these highways is an important parameter in their design and efficiency. High percentage of heavy vehicle traffic imposes adverse impacts on their capacity and level of service, particularly at the slopes. “Passenger Car Equivalent” concept is used for accounting the effect of such vehicles on service quality and highway capacity. In this research, two methods of “speed difference” and “headway” were used for determining the coefficients of “Passenger Car Equivalent”. In this research, nine two-lane highway sections were selected in different geographic, weather, topographic and volume conditions for data gathering. A new vehicle classification were proposed and used instead of the formal classification of highway transportation and maintenance organization. The obtained results were compared. The comparisons indicate that the methods give close results. In addition, the results show that obtained passenger car equivalent coefficients are generally less than the corresponding values in HCM 2010 and the difference increases with slope.