Abstract:
With ever increasing transportation demand, highway agencies are struggling to
provide reliable level of service (LOS) to the road users. Knowledge of capacity of
existing highway system is an important input for capacity enhancement decision
making. In order to determine capacity and level of service, existing methodologies make
use of concept of passenger car equivalent (PCE). PCE is used to convert a mixed traffic
stream into a base stream (passenger cars only) for the determination of traffic density
and highway capacity/LOS. Most of the existing PCE values are based on research
carried out in USA and other developed countries. Pakistan being a developing country
has traffic composition and vehicles travel characteristics considerably different from
those of developed countries. Consequently, standard traffic parameters practiced in
developed countries may not be appropriate for Pakistan. In present research, an effort
has been made to develop PCE values for different vehicle classes on the rural arterials of
Pakistan using the concept of lagging headway ratios. Video data were collected from
four different locations on Grand Trunk Road (N-5) and software package “Traffic
Tracker” was used for the extraction of necessary information from video clips of 10-
minute duration. Three-stage-least-squares (3SLS) regression model was developed to
estimate the lagging headways for passenger car (PC), passenger van (PV), single unit
truck (SUT) and combination truck (CT). The PCE values estimated for PV, SUT, and
CT are 0.94, 0.87 and 1.03 respectively. Study results revealed that passenger van has
similar travel characteristics as that of passenger car (almost similar speed and headway).
Also, there is no conclusive evidence that SUT and CT have large headways under stable
stream conditions. However, additional efforts are required to refine the estimated PCE
values for different vehicle classes on rural arterials of Pakistan using data from different
geographical locations/ highways.
