A Modified Approach for Estimation of Passenger Car Units on Intercity Divided Multilane Highways

The accuracy of measured traffic flow on a roadway is highly depends on correctness of PCUs used for converting traffic volume. Field data for the present study was collected from the mid-block road sections of different divided multilane highways in India. Video graphic method was used for collecting the field data. PCUs are estimated from the available methods as given in the literature by using traffic flow data observed in the field. Present study describes a modified methodology for estimation of PCU value of subject vehicles that includes the time headway as influencing parameter. The approach used in the present study is inspired from the method of dynamic PCU estimation where a PCU is expressed as the ratio of speed ratio and area ratio of standard cars to the subject vehicle type. Unlike dynamic PCU method, this method includes time headway factor for PCU estimation. The method found more realistic and logical as it provides relatively higher values of PCUs than those obtained from dynamic PCU method. Simulation of traffic flow was also performed through microscopic simulation model VISSIM for generating congestion and for comparing estimated PCU values at the level of maximum traffic volume. The methodology adopted in this study will be extended for development of comprehensive PCU model by including more numbers of influencing factors under varying traffic and roadway conditions