Evaluation of the Feasibility of At-Grade Crossings and Traffic Management Strategies for The Addis Ababa Light Rail Transit Corridor
Creators: name: Abel, Girma
Publisher: name: National Academic Digital Repository of Ethiopia
Year: 2015

description: Light rail transit system is being introduced in Addis Ababa. The project is a semi-exclusive alignment running along the median of roadway. It is designed to cross intersections at-grade or through grade separation facilities. Light rail generally reduce traffic congestion through the reduction of demand for vehicles, but when crossings at-grade delay is induced on the train and/or vehicles depending on factors such as: degree of priority to train, signal configuration, crossing geometry, frequency of light rail vehicles, and number of vehicles crossing. The computation of level of service of the crossing determines what kind of operation is feasible. There are three operations identified for light rail crossing: first, where light rail at-grade operation with full priority to the train is feasible; second, where light rail can operate conditionally preempted with train delays; and third, where at-grade operation is infeasible. The study identified CMC, Salitemihiret, and Adey Abeba at-grade crossing intersections of the Addis Ababa light rail transit project for operation feasibility analysis. Geometric and traffic volume data are collected at each intersection for at-grade operation feasibility analysis. Initial screening analysis indicate that the intersections can operate at-grade with full preemption to LRT till the year 2019, 2020 and 2021 for Salitemihiret, Adey Abeba and CMC intersections respectively and each intersection may operate at-grade for additional three years with conditional priority to LRT. Geometric parameters of the sites and speed profile of the train are used as inputs for further assessments of potential impact of rail operation on the crossings. Due to long crossing distances at CMC and Salitemihiret roundabouts, the train occupies the crossing for unusually longer period, 67 and 62 seconds respectively for full priority scenario, resulting in unacceptable delay on vehicles. At Adey Abeba junction crossing occupation duration, 47 seconds, is within acceptable limit. Vehicles queue accumulated during crossing blockage is computed for all direction in order to determine the required storage area of turning movements. The impact of train operation on the capacity of the intersection is checked for both full priority and conditional priority given to the train. The analyses are performed for existing and improved geometries. As per the detail analysis the optimized lane configurations are; for CMC 6 lanes along the North-South and 7 lanes along the East-West directions, for Salitemihiret 7 lanes in all directions, and for Adey Abeba 6 lanes along the North-South and 5 lanes along the East-West directions. In conclusion; at CMC roundabout full preemption with reduced crossing distance and conditional priority are feasible type of operations; at Salitemihiret conditional priority with train delay is feasible; and at Adey Abeba junction both full preemption and conditional type of operations are feasible. The study also presents the number of lanes and its configuration for each crossing; it also identifies improvements for pedestrian crossing facilities along the route.