  In this paper we propose a novel two-step linear optimization model to
calculate energy-efficient timetables in metro railway networks. The resultant
timetable minimizes the total energy consumed by all trains and maximizes the
utilization of regenerative energy produced by braking trains, subject to the
constraints in the railway network. In contrast to other existing models, which
are NP-hard, our model is computationally the most tractable one being a linear
program. We apply our optimization model to different instances of service
PES2-SFM2 of line 8 of Shanghai Metro network spanning a full service period of
one day (18 hours) with thousands of active trains. For every instance, our
model finds an optimal timetable very quickly (largest runtime being less than
13s) with significant reduction in effective energy consumption (the worst case
being 19.27%). Code based on the model has been integrated with Thales
Timetable Compiler - the industrial timetable compiler of Thales Inc that has
the largest installed base of communication-based train control systems
worldwide.
