Rafael Grosso

Selecting the location of minihubs for freight delivery in congested downtown areas

Abstract The delivery of freight in urban areas has to face many restrictions and regulations that constrain the efficient flow of goods. One of the most common regulations in medium and large cities is the establishment of access time windows, whereby delivery vehicles can only access the most central and congested areas of the city during a pre-specified period of the day. To avoid the costs imposed on carriers by this regulation while maintaining the social and environmental sustainability benefits, we propose here the establishment of a system of mini-hubs where delivery vehicles may park for the final deliveries to be completed on foot. Given that the optimal location of these mini-hubs is essential for the operation of the system, we formulate a location model and apply a computational process based on genetic algorithms to optimize it. We apply this procedure to a case study in the Spanish city of Seville, showing the effect of mini-hubs on the costs of the overall delivery system.

Estimating the extra costs imposed on delivery vehicles using access time windows in a city

Abstract Analyses performed before introducing access time window policies in the center of European cities often do not evaluate the extra costs imposed on carriers from the additional number of vehicles required and increase in tour length. To facilitate this evaluation, we have developed a vehicle routing algorithm that considers the existence of access time windows and adapts tours to this restriction in the best possible manner. The procedure is based on a genetic algorithm, which we calibrate by analyzing several experiments in a test network. We then apply the algorithm to a real case study in the city of Seville, where local authorities are considering increases in the duration of the time window restriction and the size of the restricted area.

Use of a genetic algorithm for building efficient choice designs

Choice design building based on D-error minimisation can be accomplished either by using predefined β values or by assuming probabilistic distributions for them. Several mathematical techniques have been used for both approaches in the past, resulting in algorithms that obtain efficient designs, which guarantee the high quality of the information that will be provided by the respondents. This paper proposes the use of a genetic algorithm for dealing with the problem of building designs with minimum D-error, describing the technique and applying it successfully to several benchmark cases. Design matrices, D-error values, percentages of level overlap and computation times are provided for each case.

Teaching Heuristic Methods to Industrial Engineers: A Problem-Based Experience

Because of its mathematical and computational components, operations research OR is not simple to teach or to learn, despite its innumerable industry applications. However, advanced OR is included in many graduate degrees related to industrial engineering, where students need these techniques to solve complex optimization problems. Faced with the problem of teaching heuristic methods to masters students at the University of Seville, we developed a problem-based approach whereby instead of listening to lectures and taking exams on these techniques, one algorithmic technique is randomly assigned to each student, who must apply it to solving a certain optimization problem. Here we discuss our approach to putting our heuristics course into practice, the problems we faced, how we addressed those problems, the positive results obtained, and the lessons learned.

Development of a Cost Model for Intermodal Transport in Spain

For several years, the promotion of intermodal transport has been a priority for the Spanish and European authorities (Cuerda et al., 2003; Conseil National des Transports [CNT], 2005) but the importance and the recent growth of rail transport in Spain is extremely small compared to road transport. This is more so in the case of small and medium-size companies shipping general (non-bulk) cargo, which almost exclusively use the road (Ministerio de Fomento, 2004). The establishment of a network of intermodal freight transport centres connected to the main railway lines and close to the main cities is viewed as an opportunity for the modal shift, and also the establishment of relevant intermodal corridors dedicated to specific freight purposes (ore, agricultural products), to be defined at a European level, should improve the overall figures. But nevertheless, there is the feeling in Spain that more attention should be given to general traffic issues, facing the needs of the great amount of small companies moving small amounts of freight, but with an enormous aggregate effect. Thus the strategic objectives of our work lie within the rationalization of mobility and the improvement of intermodal accessibility. They concentrate on establishing the basis for a higher participation of small and medium-size companies in intermodal transport by analyzing the specific experiences of an individual transport company, based in the city of Seville, seeking an enhancement of the modal shift within its logistic operations. This work is organized as follows: In section 2 we describe the role of intermodal transport in the supply chain. In Section 3 we list the actors involved in all phases of intermodal transport to then show the decision-making model for each one of these actors. In Section 4 we apply this model to the case of a transport company based in the South of Spain, describing all the shipment and cost data. Finally, in section 6 we explain our conclusions drawn from the decision making model in general and in particular for the case-study company, and analyze the effect of additional factors (other than cost) in the decision-making process with respect to intermodal transport.

Mathematical Formulation and Comparison of Solution Approaches for the Vehicle Routing Problem with Access Time Windows

The application of the principles of sustainability to the implementation of urban freight policies requires the estimation of all the costs and externalities involved. We focus here on the case of access time windows, which ban the access of freight vehicles to central urban areas in many European cities. Even though this measure seeks to reduce congestion and emissions in the most crowded periods of the day, it also imposes additional costs for carriers and results in higher emissions and energy consumption. We present here a mathematical model for the Vehicle Routing Problem with Access Time Windows, a variant of the VRP suitable for planning delivery routes in a city subject to this type of accessibility restriction. We use the model to find exact solutions to small problem instances based on a case study and then compare the performance over larger instances of a modified savings algorithm, a genetic algorithm, and a tabu search procedure, with the results showing no clear prevalence of any of them, but confirming the significance of those additional costs and externalities.

Estimating the effects of access time windows in the management of urban delivery fleets

The analyses prior to the introduction of access time window policies in the centre of European cities often neglect the evaluation of the extra costs imposed on carriers through the additional number of vehicles required and the increase in tour length. To facilitate this evaluation, we have developed a vehicle routing algorithm that takes into account the existence of access time windows and adapts tours in the best possible manner to this restriction. The algorithm is based on a Genetic Algorithm, which we use to make this evaluation through the analysis of several experiments in a test network.

Energetic Assessment of the Broiler Poultry Supply Chain

In the food supply chain, energy efficiency can be seen as a combination of technological and organizational efficiency, in all the stages of the food system. We describe the process to monitor and manage energy consumption in the supply chain, which consists of four steps: initial assessment, process design, and evaluation and application opportunities. We then apply the methodology to a broiler poultry manufacturer and distributor located in the South of Spain. Once the energy consumptions have been quantified and structured, we apply a comparative analysis to highlight those processes that represent the largest energy costs. We propose several actions for improvement (related to warehousing, inventory management, transportation, reverse logistics, energetic management, etc.), and evaluate the energetic situation of the company ex-ante and ex-post, using the appropriate indicators, in order to determine the degree of energy efficiency of the company.