Through Traffic Passenger Car Equivalents for Selected Signalized Intersections in Addis Ababa, Ethiopia

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Addis Ababa University


Currently, there are about 34 registered signalized intersections in Addis Ababa. As most of developing countries the capacity and level of service for these facilities is measured using manuals adopted from overseas. Among the overseas manuals the Highway Capacity Manual (HCM 2010) is the most common one. Different vehicle types occupy different spaces on the road, move at different speeds, and start at different accelerations.To adress such differences HCM(2010) has a conversion to saturation flow rate of signalized intersections in units of passenger cars per hour per lane (pc/h/ln). Currently, a PCE value of 2.0 is specified for all through heavy vehicles where no distinction is made between trucks, recreational vehicles, buses and other vehicles in the calculation of the adjusted saturation flow rate at signalized intersections. Traffic and drivers behavior in other countries may be significantly different from the situation in Addis Ababa, Ethiopia. Developing local values will minimize the errors we incur at every step of our capacity analysis due to the use of adopted manual input parameters. In this study the researcher has developed local through traffic passenger car equivalents for small busses, large busses, trucks and truck trailers on selected signalized intersections of Addis Ababa with significant number of heavy vehicles. Using drone technology as a data collection tool and deploying the headway ratio method for determining through traffic PCEs the researcher has come up with new local values. The study showed that the mean local PCEs of Small Busses are 1.49, 1.51, and 1.68 on first (inner), second (middle), and third (outer) lanes respectively. Similarly the mean local PCEs of Large Busses are 1.95, 2.20, and 1.99 on first (inner), second (middle), and third (outer) lanes respectively. Trucks on the other hand have mean local PCE values of 1.62, 1.56, and 1.44 on first (inner), second (middle), and third (outer) lanes respectively. Whereas, Truck Trailers have larger mean local PCE values which are 3.62 and 3.78 on second (middle) and third (outer) lanes respectively. Moreover, on relatively level approaches the PCEs are larger than the PCE values on down and upgrades. While, lane width has low effect on PCEs, approach width has significant effect on PCEs. Similarly, the available green time has direct relationship with the PCE values.



Passenger Car Equivalents, Saturation Flow Rate, Signalized Intersections, Headways