Dynamic Passenger Car Unit Estimation for Urban Road Midblock and Signalized Intersection under Heterogenous Traffic Stream in Jimma, Ethiopia.

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.