Optimal track utilization in electric multiple unit maintenance depots

- Build a simple model for improving the maintenance efficiency of electric multiple units in Chinese high-speed rails.
- The solution method yields the optimal track utilization in a small amount of computational time.
- A case is presented to show the real application of the method and discuss the difference caused by the track layout.

The Chinese high-speed rail network has a fast-growing number of electric multiple units (EMU) in service and is facing increasing pressure of maintaining all EMUs on-time. The capacity at an EMU maintenance depot is relevant to its track utilization rate, which can be improved by a better EMU-to-track assignment in various areas, such as the maintenance yard, temporary storage yard, and washing yard. Most tracks at EMU depots have two sections that can accommodate one long EMU of sixteen railcars or two short EMUs of eight railcars. The two yard types, stub-end and through, further add complexity to the assignment problem, which is currently handled manually. To make the assignment process more efficient, this paper proposes a simple optimization model for yards with either type and with any combination of long and short EMUs. The numerical results based on a real-world case show that the proposed solution method can yield an assignment plan with the optimal track utilization in a small amount of computational time and can be implemented in a computer-aided planning system easily. The case also discusses potential changes in practice to improve the track utilization rate, such as changing the maintenance schedule and connecting two short EMUs into a long EMU. After comparing the track utilization rates between the two yard types, the paper suggests that the through type is more appropriate for the current schedule at EMU depots, especially for the maintenance yard.