Optimizing Emergency Transportation through Multicommodity Quickest Paths

In transportation networks with limited capacities and travel times on the arcs, a class of problems attracting a growing scientific interest is represented by the optimal routing and scheduling of given amounts of flow to be transshipped from the origin points to the specific destinations in minimum time. Such problems are of particular concern to emergency transportation where evacuation plans seek to minimize the time evacuees need to clear the affected area and reach the safe zones. Flows over time approaches are among the most suitable mathematical tools to provide a modelling representation of these problems from a macroscopic point of view. Among them, the Quickest Path Problem (QPP), requires an origin-destination flow to be routed on a single path while taking into account inflow limits on the arcs and minimizing the makespan, namely, the time instant when the last unit of flow reaches its destination. In the context of emergency transport, the QPP represents a relevant modelling tool, since its solutions are based on unsplittable dynamic flows that can support the development of evacuation plans which are very easy to be correctly implemented, assigning one single evacuation path to a whole population. This way it is possible to prevent interferences, turbulence, and congestions that may affect the transportation process, worsening the overall clearing time. Nevertheless, the current state-of-the-art presents a lack of studies on multicommodity generalizations of the QPP, where network flows refer to various populations, possibly with different origins and destinations. In this paper we provide a contribution to fill this gap, by considering the Multicommodity Quickest Path Problem (MCQPP), where multiple commodities, each with its own origin, destination and demand, must be routed on a capacitated network with travel times on the arcs, while minimizing the overall makespan and allowing the flow associated to each commodity to be routed on a single path. For this optimization problem, we provide the first mathematical formulation in the scientific literature, based on mixed integer programming and encompassing specific features aimed at empowering the suitability of the arising solutions in real emergency transportation plans. A computational experience performed on a set of benchmark instances is then presented to provide a proof-of-concept for our original model and to evaluate the quality and suitability of the provided solutions together with the required computational effort. Most of the instances are solved at the optimum by a commercial MIP solver, fed with a lower bound deriving from the optimal makespan of a splittable-flow relaxation of the MCQPP

Designing a web spatial decision support system based on analytic network process to locate a freight lorry parking

The relevant role of freight lorry parking facilities as a tool to reduce nuisances and impact of economic activities in densely populated urban areas is widely recognised in the literature. Nevertheless, the literature currently lacks specific contributions addressing the use of a complex Multiple Criteria Decision Analysis (MCDA) approach for coping with an optimal location of freight lorry parking facilities in the urban context. This paper contributes to filling this gap by analysing a real-world case study motivated by the problem of intense freight vehicles traffic around the city of Bradford, Yorkshire (UK). Since it is necessary to include diverse analysis perspectives, reflecting the different classes of involved stakeholders, this study proposes adopting the Analytic Network Process (ANP) approach as a tool to support the selection and evaluation of alternatives for a freight lorry parking facility, followed by the design of software based on this approach. The proposed web Spatial Decision Support System provides a valuable tool to foster extended discussions with experts and facilitate the decision process in this class of location problems

The Spatially Equitable Multicommodity Capacitated Network Flow Problem

In this work we propose a novel approach addressing the need for a spatially equitable distribution of the flows when routing multiple commodities on a capacitated network. In our model, the spatial distribution of the flows is considered by partitioning the area in which the network is embedded by means of a grid of uniform size cells and then computing the impact of the network flows on each cell by a weighted linear combination of the flows interesting each cell. A spatially equitable distribution of the flows is therefore obtained when all the multicommodity demands are satisfied in such a way to minimize the maximum impact registered on the cells of the grid. We refer to this problem as the spatially equitable multicommodity capacitated network flow problem and propose a minimax linear programming formulation. The need to find a proper trade-off between the total routing cost and the spatial equity is treated as well by considering both the objective functions and computing pareto-optimal solutions for the bicriteria optimization problem. Computational results obtained on a real traffic network are presented and discussed in the paper. © 2011 Springer-Verlag

Service Network Design Models for Two-tier City Logistics

Abstract This paper focuses on two-tier City Logistics systems for advanced management of urban freight activities and, in particular, on the first layer of such systems where freight is moved from distributions centers on the outskirts of the city to satellite platforms'by urban vehicles, from where it will be distributed to customers by other, dedicated vehicles. We address the issue of planning the services of this first tier system, that is, select services, their routes and schedules, and determine the itineraries of the customer-demand flows through these facilities and services. We propose a general scheduled service network design modeling framework that captures the fundamental concepts related to the definition of urban-vehicle tactical plans within a two-tier distribution network. We examine several operational assumptions regarding the management of the urban-vehicle fleet, the flexibility associated with the delivery of goods, and the impact of the freight transfer operations at satellites, and show how the proposed modeling framework can evolve to represent an increasing level of detail. A discussion of algorithmic perspectives completes the paper

Optimizing Dry Port Based Freight Distribution Planning

In this paper we review the dry port concept and its outfalls in terms of optimal design and management of freight distribution. Some optimization challenges arising from the presence of dry ports in freight distribution systems are presented and discussed. Then we consider the tactical planning problem of defining the optimal routes and schedulesfor the fleet of vehicles providing transportation services between the terminals of a dry port based intermodal system. An original service network design model based on a mixed integer programming mathematical formulation is proposed to solve the considered problem. An experimental framework built upon realistic instances nspired by regional cases is described and the computational results of the model are presented and discussed