# Double-Track One-Direction Operation Mode for Overnight Trains on High-Speed Railway
## 1 Introduction  
With the increasing mileage of China's high-speed railways, mileage and coverage are also increasing. Compared with other countries with high-speed rails, China's high-speed railway has a large operation area and a long distance, and long-distance cross-line trains can make distant city connections directly. Compared to air transport, rail transport has certain advantages in terms of leaving luggage restrictions and keeping communications open, but daytime runs cannot implement the connection to extra long-distance cities, and some long-distance trips for interconnected cities, for instance, 2760 km Beijing to Kunming, leave in the morning and arrive in the evening. It takes a whole diurnal ride on trains; thus, the sunset-departure and sunrise-arrival sleeper Electric Multiple Unit (EMU) trains are favored by the majority of passengers. High-speed rail freight is more flexible than air freight in some respects. All stations along the railway can send and receive goods, and if high-speed rail freight can be carried out at night, it greatly improves the efficiency of logistics. At the same time, in order to ensure the safety, all China's high-speed railways currently arrange a daily four-hour maintenance disruption. The general maintenance disruptions are usually arranged between 00:00 and 06:00 after midnight, which limits the operation of overnight trains, and daily operation is unrealizable. More than half of250 km/h sleeper EMU trains can only run during the daytime and even in the form of'sleeper as seats', wasting the sleeping function of these trains. China's economy continues to grow, and both passenger and freight transport demand are increasing rapidly. It is the general trend to realize the overnight operation of high-speed railways. How to solve the problem of high-speed railways running overnight trains is a hot topic for scholars to study at present, with scholars focusing on the organization of train running and the optimization of maintenance disruptions' operation. In terms of operating organization, the current research mainly involved the following aspects. Three modes were discussed in [1], including waiting for maintenance disruption to finish on a high-speed railway station, which is shown in Figure 1a; transferring from a high-speed railway to conventional railways before maintenance disruption and arriving at the destination through conventional railways shown in Figure 1b; transferring to a conventional railway before maintenance disruption and then back to the high-speed railway after maintenance disruption as Figure 1c shows, and [2] compares the three methods and their applicable scene. A combination of operation modes was studied in [3], and by fusing the above three modes, a hybrid mode can be obtained as shown in Figure 1d. In addition to the above methods, the method in [4] proposed operation in a single-track during maintenance disruption, and they analyzed and compared the adaptability and  
Figure 1: Three modes and the hybrid mode in the current research. (**a**) Waiting for maintenance disruption; (**b**) transfer to conventional railways before maintenance disruption; (**c**) transfer to conventional railway then back to high-speed railway; (**d**) hybrid mode. safety. In [5], a mixed integer linear programming model was used to identify the operation modes and the timetable of sunset-departure and sunrise-arrival trains by integrating the time selection of regular maintenance on high-speed railways. A nonlinear mixed integer programming model was established in [6] to realize the collaborative optimization of overnight train operation and maintenance disruption in the condition of the undetermined train operation mode. None of these methods have been used in practice, or they have already been abandoned. Waiting for maintenance disruption on a high-speed railway station takes a long time, wastes time, and reduces cost performance.