Optimising vehicle and on-foot porter routing in urban logistics

As modern cities expand, parcel carriers are obliged to deal with the various last-mile challenges of the urban setting, in order to meet the ever-increasing requirements of consumers while ensuring an eco-friendly distribution system. Some of the urban last-mile challenges, such as kerbside parking limitations and vehicle access restrictions, pose additional constraints to carriers that operate van-based deliveries. This paper describes a new distribution model and an associated optimisation problem, namely a vehicle routing problem with portering (VRP-P) with time windows, that integrates on-foot porters with cargo vans. In this distribution strategy, vans rendezvous with porters at handover points at selected customer locations where the transfer of parcels can take place, avoiding the need for designated parking spaces. The VRP-P is modelled as a mixed-integer linear programming formulation and solved on real delivery data in central London. The paper also describes a fast heuristic that uses several improvement operators. Computational results show that the use of portering yields time and carbon savings of up to 89%, depending on the number of customers served. The heuristic obtains high-quality feasible solutions in short computational times and outperforms a commercial optimiser on large scale instances. The findings also show high utilisation of portering even at limited parcel carrying capacities