Abstract
Due to their different sizes and operational characteristics, vehicles other than passenger cars have a different influence on traffic operations especially at intersections. The passenger car equivalent (PCE) is the parameter that shows how many passenger cars must be substituted for a specific heavy vehicle to represent its influence on traffic operation. PCE is commonly estimated using headway-based methods that consider the excess headway utilized by heavy vehicles. In this research, the PCE was estimated based on the delay parameter at three signalized intersections in Tehran, Iran. The data collected were traffic volume, travel time for each movement, signalization, and geometric design information. These data were analysed and three different models, one for each intersection, were constructed and calibrated using TRAF-NETSIM simulation software for unsaturated traffic conditions. PCE was estimated under different scenarios and the number of approach movements at each intersection. The results showed that for approaches with only one movement, PCE varies from 1.1 to 1.65. Similarly, for approaches with two and three movements, the PCE varies from 1.07 to 1.99 and from 0.76 to 3.6, respectively. In addition, a general model was developed for predicting PCE for intersections with all of the movements considered. The results obtained from this model showed that the average PCE of 1.5 is similar to the value recommended by the HCM (Highway Capacity Manual) 1985. However, the predicted PCE value of 1.9 for saturated threshold is closer to the PCE value of 2 which was recommended by the HCM 2000 and HCM 2010.
Highlights
Where dm is the average delay of approach m, Vm is traffic volume of approach m, dmi is the delay of movement i in approach m, Pim is the percentage of movement i in approach m, d0 is the basic delay, and PHi is the proportion of heavy vehicles i in traffic flow
The simulation models were run at zero percent of heavy vehicles and considered the volume needed to obtain the basic delays at each approach
The zero percent heavy vehicle condition was not given in the field data, so the basic delay estimation supported the claim that the use of simulation in this study was inevitable
Summary
In 1947, Greenshields et al formulated the PCE value by dividing the average headway of heavy vehicles type over the average headway of passenger cars. This method, called the headway ratio method, is commonly used for measuring PCE at signalized intersections [5, 7]. Branston and van Zuylen developed a multiple regression method for estimating PCE at signalized intersections in 1978. In this method, vehicle departures are recorded over an arbitrary period during the green light. After the Branston and van Zuylen’s study, the multiple regression analysis method was used to drive PCE factors in many studies [6]
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