Flexible rolling stock composition strategy in urban rail transit lines: The influences of various train units and station capacities

This work studies the flexible rolling stock strategy in urban rail transit lines, by which various train units can be coupled to or uncoupled from the trains in certain stations according to the time-varying passenger demand. Due to the use of various train units, coupling and uncoupling train units must respect specific rules related to the shunting rules in adaptation stations, it is important to take into account the order of the train units in the trains. A mixed-integer linear programming model is proposed to optimize the rolling stock compositions together with the train timetable. Additionally, the model includes constraints for passenger assignment to evaluate the number of passengers in train services or stranded at stations. The model aims at reducing the number of stranded passengers, the number of rolling stocks, and the operational costs. To efficiently solve the integrated optimization problem, this study proposes an approximation approach and a two-stage heuristic algorithm. The approximation approach relaxes some calculations and constraints in an approximate manner in order to improve the computational speed. The two-stage heuristic approach divides the integrated optimization problem into two subproblems and solves the two subproblems with a heuristic searching method. The proposed optimization method is examined using the historical operation data of Shanghai Metro Line 16. The results suggest that the proposed approach can well satisfy the passenger travel demand and decrease operational costs. In addition, the influences of train unit types, headway control strategy, and station capacities are studied. The findings of the case studies can provide insights into timetable and rolling stock schedule planners. •A service-oriented optimization of rolling stock circulation and metro timetable.•The flexible rolling stock compositions are considered.•A MILP model is built to reduce the number of stranded passengers and the operational costs.•Influences of train unit types, headways, and station capacities are studied.