Xiang Li - Subway Energy-Efficient Management

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Subway is an electric passenger railway, which is operated either in underground tunnels or on elevated rails. In the past decades, the subway has received rapid development in China due to its high capacity, punctuality, and reliability. Up to June 2019, there have been 39 cities opening 174 urban rail transit lines, among which Shanghai operates the largest subway network, and Beijing operates the busiest subway network in the world. On December 30, 2017, Beijing subway Yanfang line started operation, the first domestically developed automated subway in China.

For subway operations management, the optimal train control and scheduling methods have been extensively studied with various objectives, among which energy saving has attracted much attention from both researchers and practitioners on account of the rising energy prices and environmental concerns. The most popular energy-efficient management approaches include speed control and timetable optimization; the former is a type of commonly used methods while the latter is a class of emerging method, which respectively contribute to reducing traction energy consumption and improving regenerative energy absorption.

Speed control approach optimizes the time-speed profile for trains at inter-station to minimize traction energy consumption. The literature on energy-efficient speed control can date back to the 1960s. In 1968, Ishikawa proposed the first optimal train control model to determine the most energy-efficient speed profile. After that, both theoretical analyses and heuristic algorithms have been given, among which Howlett and his Scheduling and Control Group made extraordinary contributions to laying the foundation for energy-efficient speed control theory or energy-efficient operation theory.

Timetable optimization approach synchronizes the accelerating phases and braking phases of adjacent trains located in the same substation to maximize the regenerative energy absorption. Over the past years, a series of timetable optimization models have been formulated. For example, Ramos et al. (2007) first presented a timetabling problem that aims to maximize the overlapping time between accelerating actions and braking actions of adjacent trains, so that the accelerating trains can absorb the regenerative energy from braking trains as much as possible. In 2013, Li and Yang measured the regenerative energy absorption as the integral of the minimum profile between traction energy and regenerative energy at the overlapping time and formulated an energy-efficient timetabling model.

Essentially, timetable optimization and speed control are two closely related processes on energy saving. The timetabling process allocates the travel time among inter-stations, which significantly influences the traction energy consumption, while speed control process determines the accelerating time and braking time at inter-stations, which profoundly influences the regenerative energy absorption. Therefore, some researchers studied the integrated optimization on timetable and speed profile to minimize the net energy consumption, i.e., the difference between traction energy consumption and regenerative energy absorption. For example, Li and Lo (2014) proposed a mixed integer programming model and designed a genetic algorithm to minimize the net energy consumption, which integrally optimizes the accelerating time and braking time at inter-stations, dwell time, cycle time, and trip frequency. As extensions, the dynamic optimization methods and stochastic optimization methods on timetable and speed profile were also studied.

The purpose of this book is to provide a powerful tool to handle the subway energy-efficient management problems. It provides a comprehensive presentation on train timetable optimization and speed control models with the objective of energy saving. The methods presented here are designed for but not limited to the subway system. It can be extended and applied to the timetabling and speed control for high-speed trains and other types of passenger trains. The book is suitable for researchers, engineers, and students in the fields of transportation science, management science, and so on. The readers will learn numerous new modeling ideas on reducing traction energy consumption and improving regenerative energy absorption and find this work a useful reference.