An ANTS Heuristic for the Long – Term Car Pooling Problem Vittorio Maniezzo 1 , Antonella Carbonaro 1 , Daniele Vigo 2 , Hanno Hildmann 3 1 Department of Computer Science, University of Bologna, via Sacchi 3, 47023 Cesena, Italy {maniezzo,carbonar}@csr.unibo.it 2 DEIS, University of Bologna, Viale Risorgimento 2, 40136 Bologna, Italy dvigo@deis.unibo.it 3 Departement of Science, University of Amsterdam, Plantage Muidergracht 24, 1018 TV Amsterdam hhildman@science.uva.nl Abstract The rising auto usage deriving from growth in jobs and residential population is making traffic congestion less tolerable in urban and suburban areas. This results in air pollution, energy waste and unproductive and unpleasant consumption of people’s time. Public transport cannot be the only answer to this increasing transport demand. Car pooling has emerged to be a viable possibility for reducing private car usage in congested areas, however its actual practice requires a suitable information system support and, most important, the capability of effectively solving the underlying combinatorial optimization problem. This paper presents an application of the ANTS approach, one of the approaches which follow the Ant Colony Optimization (ACO) paradigm, to the car pooling optimization problem. Computational results are presented both on VRP-derived standard datasets and on real-world instances. 1 Problem description The rising auto usage deriving from growth in jobs and residential population is making traffic congestion less tolerable in urban and suburban areas. Traffic results in air pollution, energy waste and unproductive and unpleasant consumption of people’s time. Public transport cannot be the only answer to this increasing transport demand, and it becomes necessary to develop alternative mobility systems which can provide intermediate solutions, in terms of costs and flexibility, between public transport and private cars. Among the most promising solutions so far tested are the car pooling and car sharing services, which have shown to have the potentiality to attack a mobility segment badly satisfied by public transport. Car pooling is a mobility service proposed and controlled by large organizations, such as large companies or public administrations, which encourage their citizens or employees to pick up colleagues while driving to/from work in order to minimize the number of private cars traveling to/from a common destination site. The benefits which can be obtained are particularly relevant both in terms of reduction of the use of private vehicles and of the parking space required. The car sharing option considers the