Simulation Models to Evaluate Railway Operating Policies

In this paper, we describe two applications of simulation models to evaluate the following railway operating policies: 1. Loco assignment at a junction, and 2. Twin single line versus orthodox double line operation. The models are developed as a part of a project for improving resource utilization in a zonal railway of the Indian Railways. Loco assignment at a junction: at a junction, a large number of iron ore trains go loaded in one direction and return empty in the other. These trains form a major proportion of a steam of trains, consisting of a view non-iron trains also. For this stream, the track on one side of the junction is electrified while the other side is not. Diesel traction is used on the non-electrified side, with double heading in the loaded direction, (which is towards the junction for iron ore trains), and single heading in the empty direction, (away form the junction for iron ore trains). This creates a surplus of diesel locos at the junction, which are sent light for other uses. The simulation model evaluates the rules for assignment of locos for light running. The operating rule considered is for how time an incoming diesel loco should wait for being assigned to a train. If no train is expected within the stipulated time, the loco is sent light. The criterion used for evaluating different values of the above parameter is the minimization of the total waiting costs of locos and trains. This is derived by first computing the waiting time incurred by all locos and trains, and then finding the weighted sum by using relative weights of loco and train waiting costs. Twin single line versus orthodox double line operation: A 43 km, orthodox double line section of a busy main line, apart from catering to through traffic, has five originating/terminating stations for coal and cement movements. These movements further necessitate empty train movements, light engine movements, and movements for maintenance. Some of the facilities such as coal loading points and wagon maintenance depot are so located that the trains accessing these facilities cause cross movements, resulting in detention. A suggested solution to this problem is to convert the section to a twin single line operation, which provides flexibility in scheduling cross movements. An added advantage of twin single line operation could be in better utilization of track capacity during a period when there are successive trains in the same direction. Since, the above proposal involves high capital investment, it is essential to evaluate the effect of the proposed conversion on line capacity and average section travel time. For this, an existing simulation model, developed to measure line capacity on a different section, is being extended. The paper summarizes the existing model and its extension.