On the Benefits of Inoculation, an Example in Train Scheduling

TL;DR

This paper introduces an inoculation method that enhances an evolutionary algorithm for train scheduling by initializing it with pre-computed solutions, significantly improving performance on large real-world instances and reducing delays.

Contribution

The paper presents a novel inoculation procedure that improves evolutionary train re-scheduling algorithms using problem-related initial solutions, leading to better optimization results.

Findings

Inoculation improves algorithm success rate on large instances.

Pre-initialized solutions outperform random starts in scheduling.

Method achieves competitive results against commercial solvers.

Abstract

The local reconstruction of a railway schedule following a small perturbation of the traffic, seeking minimization of the total accumulated delay, is a very difficult and tightly constrained combinatorial problem. Notoriously enough, the railway company's public image degrades proportionally to the amount of daily delays, and the same goes for its profit! This paper describes an inoculation procedure which greatly enhances an evolutionary algorithm for train re-scheduling. The procedure consists in building the initial population around a pre-computed solution based on problem-related information available beforehand. The optimization is performed by adapting times of departure and arrival, as well as allocation of tracks, for each train at each station. This is achieved by a permutation-based evolutionary algorithm that relies on a semi-greedy heuristic scheduler to gradually reconstruct the schedule by inserting trains one after another. Experimental results are presented on various instances of a large real-world case involving around 500 trains and more than 1 million constraints. In terms of competition with commercial math ematical programming tool ILOG CPLEX, it appears that within a large class of instances, excluding trivial instances as well as too difficult ones, and with very few exceptions, a clever initialization turns an encouraging failure into a clear-cut success auguring of substantial financial savings.