Calibrating Passenger Car Equivalent (PCE) for Highway Work Zones using Speed and Percentage of Trucks

In the Highway Capacity Manual (HCM 2000), capacity is expressed as the unit passenger cars per hour per lane (pcphpl). The number of passenger cars a single vehicle is equivalent to is the passenger car equivalent (PCE). This paper studied PCEs within highway work zones that were based upon the speed and the percentage of trucks. The results indicated that PCEs designated for highway work zones have their own distinct characteristics. This study plotted 3 dimensional charts to display the change of PCEs with respect to the speed and percentage of trucks. Thus, a
mountain chain of PCEs is formed on the speed-percentage (percentage of truck traffic) plane. The 3 dimensional charts help identify the PCE value as speed varies given the same percentage of truck traffic or as the percentage of truck traffic changes given the same speed. First, the multiple regression (the traditional method) was implemented to identify the relationship among PCEs, speed and percentage of truck traffic. Then, a new closed-loop approach was introduced in this paper to estimate
PCEs using collected work zone data, which is totally different from traditional methods. It was also found that the closed-loop approach could help remove the error caused by a critical factor whose impact is usually ignored by traditional methods. Finally, more detailed PCE values for short-term and long-term work zones are tabulated in a compatible format similar to that used in the HCM (2000).