Earth Potential as the Energy Storage in Rail Transit System - On a Vertical Alignment Optimization Problem

To increase the energy efficiency of railway transit system, train driving and scheduling strategies are widely studied. In this paper, inspired by the construction and planning of existing rail transit system and the energy storage technology, we present a novel model from a perspective that considers the earth as an on-board energy storage device which can release the potential energy and store the potential energy when the train runs in the section. By making the most of the gravity, the model can concurrently optimize the vertical alignment between two adjacent rail transit stations and its corresponding speed trajectory for reducing the traction energy consumption. The whole route between two adjacent stations are discretized and Mixed Integer Linear Programming (MILP) is applied for optimization. Specific cases such as same stations elevation and different stations elevation are studied in this paper. The results show that the proposed model can efficiently optimize the gradient, downhill length, uphill length, depth of the vertical alignment as well as the optimal speed trajectory according to the given elevation difference of the departure station and arrival station and other engineering and operational constraints. The integrated model can be used in rail transit planning and designing stage to support decision making.