Gianpaolo Ghiani

Real-time vehicle routing: Solution concepts, algorithms and parallel computing strategies

Abstract In real-time fleet management, vehicle routes are built in an on-going fashion as vehicle locations, travel times and customer requests are revealed over the planning horizon. To deal with such problems, a new generation of fast on-line algorithms capable of taking into account uncertainty is required. Although several articles on this topic have been published, the literature on real-time vehicle routing is still disorganized. In this paper the research in this field is reviewed and some issues that have not received attention so far are highlighted. A particular emphasis is put on parallel computing strategies.

Parallel Tabu search heuristics for the dynamic multi-vehicle dial-a-ride problem

In the Dial-a-Ride problem (DARP) users specify transportation requests between origins and destinations to be served by vehicles. In the dynamic DARP, requests are received throughout the day and the primary objective is to accept as many requests as possible while satisfying operational constraints. This article describes and compares a number of parallel implementations of a Tabu search heuristic previously developed for the static DARP, i.e., the variant of the problem where all requests are known in advance. Computational results show that the proposed algorithms are able to satisfy a high percentage of user requests.

A branch-and-cut algorithm for the Undirected Rural Postman Problem

Abstract.The well-known Undirected Rural Postman Problem is considered and a binary linear problem using new dominance relations is presented. Polyhedral properties are investigated and a branch-and-cut algorithm is developed. Extensive computational results indicate that the algorithm is capable of solving much larger instances than previously reported.

An efficient transformation of the generalized vehicle routing problem

Abstract The Generalized Vehicle Routing Problem (GVRP) is the problem of designing optimal delivery or collection routes, subject to capacity restrictions, from a given depot to a number of predefined, mutually exclusive and exhaustive clusters. In this paper we describe an efficient transformation of the GVRP into a Capacitated Arc Routing Problem (CARP) for which an exact algorithm and several approximate procedures are reported in literature. It constitutes the only known approach for solving the GVRP.

Review: Operations research in solid waste management: A survey of strategic and tactical issues

Solid waste management (SWM) is an increasingly complex task, absorbing a huge amount of resources and having a major environmental impact. Computerized systems based on operations research techniques can help decision makers to achieve remarkable cost savings as well as to improve waste recovery. Nevertheless, the literature is quite scattered and disorganized. The objective of this paper is to present an updated survey of the most relevant operations research literature on SWM, mainly focusing on strategic and tactical issues. In addition to providing an extensive bibliographic coverage, we describe the relationships between the various problems, and outline future research.

Rolling-horizon and fix-and-relax heuristics for the parallel machine lot-sizing and scheduling problem with sequence-dependent set-up costs

In this paper we develop new rolling-horizon and fix-and-relax heuristics for the identical parallel machine lot-sizing and scheduling problem with sequence-dependent set-up costs. Unlike previous papers, our procedures are based on a compact formulation relying on the hypotheses of identical machines. This feature makes our approach suitable for large-scale applications (with hundreds of machines) arising in the textile and fiberglass industries. Moreover, our procedures are shown to provide a feasible solution for any feasible instance. Comparisons with lower bounds provided by a truncated branch-and-bound show that the gap between the best heuristic solution and the lower bound never exceeds 3%.

The Capacitated Arc Routing Problem with intermediate facilities

This article introduces the Capacitated Arc Routing with Intermediate Facilities (CARPIF), a variant of the classical Capacitated Arc Routing Problem (CARP) in which the vehicle may unload or replenish at intermediate facilities. Two lower bounds are developed for the CARPIF: The first is based on the Rural Postman Problem (RPP) and the second one uses a relaxation of an integer linear formulation of the problem. Two upper bounds are also developed, based on the solution of an RPP and of a CARP. Computational results on a set of benchmark instances confirm the quality of the proposed bounds.

A multi-modal approach to the location of a rapid transit line

Abstract The location of a rapid transit line (RTL) represents a very complex decision problem because of the large number of decision makers, unquantifiable criteria and uncertain data. In this context Operational Research can help in the design process by providing tools to generate and assess alternative solutions. For this purpose two bicriterion mathematical programming models — the Maximum Coverage Shortest Path model and the Median Shortest Path model — have been developed in the past. In this paper a new bicriterion model, which can evaluate in a more realistic way the attractivity of an RTL is introduced. To calculate an estimation of the non-inferior solution set of the problem, a procedure based on a k -shortest path algorithm was developed. This approach was applied to a well-known sample problem and the results are discussed and compared with those obtained using a Median Shortest Path model.

Some personal views on the current state and the future of Locational Analysis

In this paper a group of participants of the 12th European Summer Institute which took place in Tenerife, Spain in June 1995 present their views on the state of the art and the future trends in Locational Analysis. The issues discussed include modeling aspects in discrete Location Theory, the influence of the distance function, the relation between discrete, network and continuous location, heuristic techniques, the state of technology and undesirable facility location. Some general questions are stated regarding the applicability of location models, promising research directions and the way technology affects the development of solution techniques.

THE CAPACITATED PLANT LOCATION PROBLEM WITH MULTIPLE FACILITIES IN THE SAME SITE

Abstract In this paper, we introduce the capacitated plant location problem (CPLP) with multiple facilities in the same site (CPLPM), a special case of the classical CPLP where several facilities can be opened in the same site. Applications of the CPLPM arise in a number of contexts, such as the location of polling stations. Although the CPLPM can be modelled and solved as a standard CPLP, this approach usually performs very poorly. In this paper we describe a novel Lagrangean relaxation and a tailored Lagrangean heuristic that overcome the drawbacks of classical procedures. These algorithms were used to solve a polling station location problem in Italy. Computational results show that the average deviation of the heuristic solution over the lower bound is less than 2%. Scope and purpose This paper deals with a location problem that is of utmost importance for many public and private organizations. The problem aims at determining a set of capacitated facilities (warehouses, plants, polling stations, etc.) in such a way that the sum of facility construction costs and transportation costs is minimised. Unlike previous papers we allow multiple facilities in the same site. As classical lower and upper bounding procedures perform very poorly in this case, we devised a novel Lagrangean relaxation and a tailored Lagrangean heuristic. Our study was motivated by a real-world application arising in Italian municipalities where one has to locate polling stations and to assign voters to polling stations.