A Constraint Programming Approach for Non-Preemptive Evacuation Scheduling

TL;DR

This paper introduces a novel constraint programming model for non-preemptive evacuation scheduling that optimizes flow and phasing, ensuring practical, timely evacuation plans with near-optimal efficiency.

Contribution

It is the first to develop a constraint-based model for non-preemptive evacuation scheduling, addressing practical constraints ignored by previous preemptive algorithms.

Findings

Schedules are generated within seconds.

Results are within 6% of optimal preemptive solutions.

Approach effectively balances evacuation efficiency and practicality.

Abstract

Large-scale controlled evacuations require emergency services to select evacuation routes, decide departure times, and mobilize resources to issue orders, all under strict time constraints. Existing algorithms almost always allow for preemptive evacuation schedules, which are less desirable in practice. This paper proposes, for the first time, a constraint-based scheduling model that optimizes the evacuation flow rate (number of vehicles sent at regular time intervals) and evacuation phasing of widely populated areas, while ensuring a nonpreemptive evacuation for each residential zone. Two optimization objectives are considered: (1) to maximize the number of evacuees reaching safety and (2) to minimize the overall duration of the evacuation. Preliminary results on a set of real-world instances show that the approach can produce, within a few seconds, a non-preemptive evacuation schedule which is either optimal or at most 6% away of the optimal preemptive solution.