Giovanni Storchi

Models for Evaluating and Planning City Logistics Systems

City logistics aims to reduce the nuisances associated to freight transportation in urban areas while supporting their economic and social development. The fundamental idea is to view individual stakeholders and decisions as components of an integrated logistics system. This implies the coordination of shippers, carriers, and movements as well as the consolidation of loads of several customers and carriers into the same environment-friendly vehicles. City logistics explicitly aims to optimize such advanced urban transportation systems. We focus on a challenging city logistics planning issue, the integrated short-term scheduling of operations and management of resources, for the general case involving a two-tiered distribution structure. We investigate the main issues related to the problem, introduce a new problem class, propose both a general model and formulations for the main system components, and identify promising solution avenues.

Shortest viable path algorithm in multimodal networks

We consider an approach using label correcting techniques to find the shortest viable path from an origin to a destination, in a multimodal transportation network. A path is called viable if its sequence of modes is feasible with respect to a set of constraints. We present an ad hoc modification of the Chronological Algorithm to solve the multimodal shortest viable path problem. We show the resulting paths of an application on a network, for different number of modal transfers. Since the results are a solution set, the choice of a path depends on the users preferences with respect to cost and number of modal transfers.

Multiperiod integrated routing and scheduling of World Food Programme cargo planes in Angola

This paper deals with the weekly planning of WFP emergency deliveries of food aid by air in Angola, where planes are required to travel back and forth between depots and clients, deliver entire loads to the client reached every time and, at night, park at a depot, subject to parking space availability. An ILP model has been formulated, called the VRVDFL model, tailored for the real problem, and has been solved. The computational experience is reported.

SHORTEST VIABLE HYPERPATH IN MULTIMODAL NETWORKS

Abstract In this work both the multimodal hypergraph and the viable hyperpath conceptualizations are presented. The shortest viable hyperpath problem (SVHP) in a multimodal transportation network is defined. We consider a label correcting approach to find the shortest viable hyperpath from an origin to a destination, for different values of the upper limit of modal transfers. Such hyperpaths compose a Pareto-optimal set, from where the user could choose the “best” hyperpath according to personal preferences with respect to the expected travel time and the upper limit of modal transfers. An application example on a multimodal network is presented.

Finding the ℓ-core of a tree

An l-core of a tree T = (V,E) with |V|= n, is a path P with length at most l that is central with respect to the property of minimizing the sum of the distances from the vertices in P to all the vertices of T not in P. The distance between two vertices is the length of the shortest path joining them. In this paper we present efficient algorithms for finding the l-core of a tree. For unweighted trees we present an O(nl) time algorithm, while for weighted trees we give a procedure with time complexity of O(nlog2n). The algorithms use two different types of recursive principle in their operation.

The location of median paths on grid graphs

In this paper we consider the location of a path shaped facility on a grid graph. In the literature this problem was extensively studied on particular classes of graphs as trees or series-parallel graphs. We consider here the problem of finding a path which minimizes the sum of the (shortest) distances from it to the other vertices of the grid, where the path is also subject to an additional constraint that takes the form either of the length of the path or of the cardinality. We study the complexity of these problems and we find two polynomial time algorithms for two special cases, with time complexity of O(n) and O(nℓ) respectively, where n is the number of vertices of the grid and ℓ is the cardinality of the path to be located.The literature about locating dimensional facilities distinguishes between the location of extensive facilities in continuous spaces and network facility location. We will show that the problems presented here have a close connection with continuous dimensional facility problems, so that the procedures provided can also be useful for solving some open problems of dimensional facilities location in the continuous case.

Efficient algorithms for finding the (k, l)‐core of tree networks

Given a tree T = (V, E), with |V| = n, we consider the problem of selecting a subtree with at most k leaves and with a diameter of at most l which minimizes the sum of the distances of the vertices from the selected subtree. We call such a subtree the (k, l)-core of T. We provide two algorithms; the first one for unweighted trees has time complexity of O(n2), whereas the second one for weighted trees has time complexity of O(n2log n). The idea for both the algorithms is that, by starting from the tree T, we construct new rooted trees where the maximum length of a path is at most l. Then, for each new tree, we can apply a greedy-type procedure to find a subtree containing the root with at most k leaves and which minimizes the sum of the distances.

Hybrid genetic algorithm to approach the DARP in a demand responsive passenger service

Abstract In this work, we address a Demand Responsive Transport System capable of managing incoming transport demand using a solution architecture based on a two- stage algorithm to solve a Dial-a-Ride Problem instance. In the first stage, a constructive heuristic algorithm quickly provides a feasible solution to accept the incoming demand. The algorithm in the second stage is a specialized Hybrid Genetic Algorithm that attempts to improve the solution evaluated at the first stage by using the time between two consecutive transportation events.

Optimizing blood assignment in a donation-transfusion system

A multi-product, multi-period, multi-objective linear programming model has been built as a contribution to good management of a blood donation‐transfusion system in order to determine the best assignment of blood resources to demand, which minimizes the quantity of blood imported from outside the system and stabilizes the quantities assigned daily. The model has been applied to the Italian Red Cross (CRI) blood donation‐transfusion system in Rome and to each hospital belonging to such a system, producing interesting results.

Paths with minimum range and ratio of arc lengths

Two new path problems in graphs are studied: MINRANGE, i.e., find a path from a vertex s to a vertex t with the smallest possible range of arc lengths, and MINRATIO, i.e., find such a path for which the ratio of the largest to the smallest arc length is minimum. Several bicriterion extensions of these problems are also considered.