A Matheuristic for the Dial-a-Ride Problem

The Dial-a-Ride is a transport system on demand. A fleet of vehicles, without fixed routes and schedules, carries people from their pickup points to their delivery points, during a pre-specified time interval. It can be modeled as an NP-hard routing and scheduling problem, with a suitable mixed integer programming formulation. Exact approaches to this problem are too limited to tackle real-life instances: time dependent network, requests received on-line, different objective functions. In this paper we propose an algorithm to solve the off-line Dial-a-Ride Problem (DARP), based on a Granular Tabu Search method. This algorithm was fast and effective, when tested on instances created ad hoc using the Milan network.