Capacity And Passenger Car Unit Estimation For Heterogeneous Traffic Stream Of Trunk Roads

The study was conducted on capacity and passenger car unit estimation for heterogeneous trafficrnstream of trunk roads on Addis Ababa to Holeta, Addis Ababa to Sendafa, Addis Ababa to Sulultarnand Addis Ababa to Sebata road sections to estimate the PCU for different categories of vehicles,rnto analyze the variation of PCU values with respect to different interval of traffic volume, torncompare and contrast the PCU resulted by Chandra’s and Homogenization coefficient methodsrnand to estimate the road capacity. Different vehicle types occupy different spaces on the road,rnmove at different speeds and start at different speeds. Especially in Ethiopia, this poses a problemrnwhen designing roads. A uniform measurement of vehicles is necessary to estimate the trafficrnvolume and the capacity of roads with mixed traffic. This is difficult to achieve unless the differentrnvehicle types are expressed in terms of a common standard vehicle unit. To attain these objectivesrnon basic segment in flat terrain of selected study road sections, the data were collected by meansrnof video recording by selecting favorable area on the study area. Depending on the concept of ERArnmanual, the vehicles are classified as standard car, 4WD, bus, truck and three wheeler. For eachrnvehicle, data such as, vehicle class; number of vehicles and travel time were measured from vehiclerntravelled in study section between two thick white lines marked across the road width to providernreference line to arriving vehicles. The measured travel time was averaged for a fifteen minuterntime interval to determine the average mean speed. Density was computed from number of vehiclerncounted in given time interval and vehicle speed. The dimension of vehicles was obtained byrnphysical measuring of the size of vehicles. From obtained data, traffic simulation were simulatedrnby PTV VISSIM software and analyzed using SPSS and MS. Excel. The results indicate that, thernPCU values for different types of vehicles were found to be different for different intervals ofrntraffic volume. The result showed that value of PCU was decreasing as the volume of the roadrnsections increase for all vehicles, except for three wheelers. The PCU resulted by Chandra’srnmethod for 4WD, bus, truck and three wheeler are (1.43, 3.96, 4.63 and 0.64) were greater thanrnthe PCU value resulted by Homogenization coefficient methods (1.27, 2.7, 3.13, 0.85) respectivelyrnfor all types of vehicles, except for three wheelers. The Capacity of the trunk road was obtainedrnfrom the average PCU by using Green shield’s Model and Greenberg model for all road sectionrndepending on the direction of flow. The capacity resulted on each sections was lower than thernvalue stated on the highway capacity manual 2010.

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