Railway capacity: A review of analysis methods

Railway capacity is seemingly easy but truly complex concept due to its interaction with all the pillars of railways such as infrastructure, rolling stock, signaling and operation planning. Efficient capacity utilization is critical for railways worldwide but the literature lacks a comprehensive survey. This paper for the first time summarizes major research that have been done in the past two decades with more emphasis on those that have been published since 2010. Over 60 papers have been examined and their contributions are summarized. At first, definitions of capacity are presented followed by major factors affecting capacity utilization. Capacity assessment methods are classified into 3 categories of analytical, optimization and simulation. Analytical methods include two main approaches of UIC 406 and CUI that compress the timetable to identify how much capacity is utilized. These methods have been developed further by some researchers. Optimization models define objective functions and operational constraints of railway network. These models can be solved exactly by any generic optimization software or metaheuristic methods needs to be applied if the size of model is large. Capacity analysis by simulation are mostly done by special railway software that can mimic intrinsic real world operational conditions.