Characterization of heavy vehicle headways in oversaturated interrupted conditions: Towards development of passenger car equivalency factors

Abstract

Passenger car equivalency (PCE) of heavy trucks is often studied using filed observation and microscopic simulation models, especially for signalized intersections. While the Highway Capacity Manual recommends a single value regardless of the percentage of those heavy vehicles, literatures have shown that this equivalency is affected by different factors, including the trucks percentage. This research aims to examine the PCE under different level of traffic and heavy trucks demands. First, field measurements were collected and used to examine the characteristics of heavy vehicle and passenger car headways in oversaturated interrupted flow conditions. Field observations were then used to calibrate a microscopic simulation model. The model was then used to evaluate impact on headways of different levels of congestion and heavy vehicle percentages. Field results show that truck headways are about 2.3 those of passenger cars. The results also show that trucks are 1.5 more likely to be first in a queue when compared to passenger cars and 1.7 times more likely to be in first four vehicles in a standing queue. Passenger cars immediately behind trucks had longer than average headway. The simulation results suggest that PCE increases nonlinearly with increase in congestion level and with percentage of trucks; PCE's increase becomes less marked once sever congestion (stop-and-go with increasing queue lengths) conditions set in.

Keywords

• Passenger car equivalency
• Heavy vehicles
• Congested traffic
• Signalized intersections
• Microsimulation