Abstract:
This study was conducted to estimate passenger car unit (PCU) of vehicles at urban road
midblock section and signalized intersection under heterogeneous traffic system in Jimma
city, Ethiopia. Traffic flow is heterogeneous in nature and its heterogeneity degree varies
from nations to nations; usually more for developing nations. This heterogeneity in traffic
causes the main challenges of traffic analysis and facility design unless it is converted into
equivalent homogeneous traffic stream using proper passenger car unit determined at
local setting. However, Ethiopian traffic engineers and transportation planners has used
passenger car unit values adopted in highway capacity manual for transportation facility
design, operational analysis and capacity estimation, which is not represents local
roadway condition. Even though, many researchers estimated passenger car unit, they
were exaggerated the values. The main objective of this study was to estimate passenger
car unit of vehicle types at midblock road section and signalized intersection under
heterogeneous traffic stream that represents a local roadway condition through
incorporate optimization method in analysis. Data were collected from purposively
selected two flat terrain midblock road section and pre-timed signalized intersection
through video recording, measurement and observation method during a peak-hour. The
passenger car units were estimated for vehicles; three-wheeler, standard car, four-wheel
drive, bus and truck at mid-block section and pre-timed signalized intersection using three
analysis methods. Firstly, analytical method; speed based and headway ratio were applied
at midblock section and signalized intersection, respectively. Secondly, microscopic
simulation analysis using Vissim software was carried out to validate analytical results.
Thirdly, optimization was applied to optimize PCU between analytical and simulation
method. Optimization method resulted passenger car unit for three-wheeler, four-wheel
drive, bus and truck as 0.65, 1.39, 2.80, 3.60 at midblock while 0.64, 1.30, 2.56, 3.29 at
signalized intersection in considering local roadway condition. These values are higher
than the adopted values in highway capacity manual (HCM 2010), but lower than the
recommended value in different literatures. Therefore, the researcher has recommended
the future researchers, designers and planners to follow such analysis methods rather than
totally using the adopted one since the PCU value for a vehicle type depends on different
parameters of the existing roadway and traffic flow behaviors.
