Route Allocation Problem And Buffer Times At Large-Scale Passenger Rail Stations

The large-scale passenger rail stations are normally the bottlenecks of executing the scheduled train services, such as the Guangzhou station, Wuhan Station Zhengzhou station, Beijing station and Chengdu station. The infrastructure needed by the scheduled arrival and departure events must be available and some level of service should be achieved. The level of service tends to decrease when the scheduled trains increase and the arrival/departure delays occur when station capacity can not satisfy the trains demand. However, the delay-tolerances for two routing schemes might be different when there is surplus station capacity. Therefore, close attention should be paid to achieving delay-tolerable routing schemes.Routing trains through rail stations is a sub-problem of scheduling passenger trains, and the aim of the Route Allocation Problem (RAP) is to allocate platforms and conflict-free inbound/outbound routes to trains while satisfying the specific train operation guidelines and ensure the station operation safety. The RAP is imposed on many temporal and spatial constraints which are caused by train timetable and station layout. The existing objectives include maximizing the total weight of train grade, maximizing the effectiveness of the platform tracks, maximizing the total weight of routes and minimizing the total delays. Some literatures mention that there is an internal delay-tolerable ability for each Route Allocation Solution (RAS). However, the problem of finding delay-tolerable RAS is rarely investigated. So, the overall objective of the RAP is to find one or some robust RAS taking consider of stochastic disturbances to trains in real-life operations.A hierarchical approach is adopted to tackle the above RAP and the expected results are obtained. Firstly, the constraints satisfying model of the RAP is built and the blocking times of the arrival and departure events are embedded in the model by train movement calculation. Secondly, a group of quantitative indices are put forward to evaluate the obtained RAS from the above model and a RAS from other approaches can also be evaluated according to the proposed indices. Then, a simulation models is constructed to analyze the delay-tolerance of the above solutions. Finally, the feasibility of locally optimizing a RAS is discussed based on the evaluation of the RAS. The main contents of the thesis are summarized as follows.(1) The time-windows overlapping model for arrival and departure events of trains is constructed. The blocking times of the events are achieved by the train movement calculation and the relation of the time-windows for two events can be made clear. The arrival and departure events of trains can be divided into some cliques and the essence of the RAP is to resolve the routes conflicts between any two events in a clique. Therefore, the RAP can be decomposed into small parts by means of the here proposed model.(2) The constraints satisfying model of the RAP is constructed and the heuristic searching for constraints programming (CP) is exploited to resolve the temporal conflicts among arrival and departure events. The constraints are divided into hard and soft ones. The former states the minimum interval between two events accessing the same platform-track and the constraints on two events accessing the same track section in throat areas, while the latter indicates the preference, including the constraints form the up-down rule, trains grade, trains connection and locomotives plans. Three steps, detecting constraints, ordering values and backtracking are followed to resolve the model.(3) A group of quantitative indices is proposed to evaluate the obtained RAS. The indices cover the platform-tracks preference, the number of buffer times, the minimum buffer time and the infrastructure utilization. The platform-tracks preference indicates the level of service of trains. Two events are totally parallel if there is no buffer time between them, while the buffer time means the maximal perturbation which the former event can bear and will not cause delay propagation, therefore the number of buffer times is the number of potential conflicts in a RAS. The minimum buffer time means the weakest part of a RAS. The bottleneck area in the station layout can be discovered by means of the infrastructure utilization.(4) The dynamic model of RAS is developed by the colored timed Petri Nets (CTPN) technology to simulate dynamic behavior of RAS. The train activity model, the single and double train model, and the hierarchical model for large-scale station layout are established. The buffer times are embedded in the model, and the bottlenecks in a RAS can be detected and some indices about delay propagation are also achieved by performing disturbances analysis.(5) The cases study indicates that the buffer times is the root determining the delay-tolerance of a RAS and the finding provide data support to optimize a RAS locally and to make shunting plans. The cases based on a practical station layout with 1045 routes and a one-hour timetable show that the minimum buffer times in two RAS obtained by WNPP and CP are 17 seconds and 188 seconds. The average departure delays for the RAS obtained by CP is 35.07% less than that for the RAS achieved by WNPP when they suffer an average disturbance of 360 seconds. So, CP is an effective approach to resolve the RAP and can obtain relatively robust solutions.