Rake linking for suburban train services

In the planning of operations in suburban train services, an important issue is rake linking. In this, physical train units called rakes (in this context, a standardized set of cars, including motor coaches in their composition) are to be assigned to services that are planned as part of the timetable. Doing this optimally (with as few rakes as possible or with as little empty running as possible) has a significant impact on the overall costs and reliability of the services. We have modeled this problem as a network flow problem and implemented it on a real life operation (Western Railway, in Mumbai). This exercise also generates rake cycles which describe the sequence of services to be done by each rake, and a perturbation analysis on parameters to identify actions for improvement. A subsequent decision is the allocation of platforms and stabling lines at terminals. The Rake Linker has been tested on a service network involving more than a thousand services on Western Railway on the Mumbai suburban railway network.