Christine Vanovermeire

Efficient metaheuristics to solve the intermodal terminal location problem

The objective of the intermodal terminal location problem is to determine which of a set of potential terminal locations to use and how to route the supply and demand of a set of customers (representing zones of supply and demand) through the network (by both uni- and intermodal transport) so as to minimize the total cost. Two different metaheuristic procedures are developed that both consist of two phases: a solution construction phase (either GRASP or attribute based hill climber) and a solution improvement phase based on local search. Innovative in this approach is the integration of a fast heuristic procedure to approximate the total cost given the set of open terminals. Both metaheuristics are compared to the results of an MIP solver. A thorough performance assessment uncovers that both metaheuristics generate close-to-optimal solutions in very short computing times. An argument in favor of the ABHC approach is that it is parameter-free and hence more transparent and likely to be accepted in a business or policy environment.

Horizontal logistics collaboration: decreasing costs through flexibility and an adequate cost allocation strategy

When entering a horizontal logistics alliance, companies can expect a significant cost decrease. In this paper, we show that when the partners in an alliance adopt a flexible attitude (i.e. allow changes to the terms of their deliveries), the total cost can be further decreased. We argue that the method used to allocate the total cost to the different partners should therefore encourage such flexibility. A case study of three companies in Belgium achieves a 25.83% decrease in transportation costs. Allocating this collaborative gain with the Shapley value, the individual gains range from 19.01% to 37.56%. By allowing changes to delivery dates and allowing large orders to be split into several deliveries, the partners in the alliance can increase the collaborative gain and their individual gains. The Shapley value is found to encourage flexibility.

Bi-objective optimization of the intermodal terminal location problem as a policy-support tool

Determining the optimal layout of an intermodal terminal network, more specifically the optimal locations of the terminals, is a complicated matter that requires adequate decision support tools. In this paper, a bi-objective model is developed, minimizing both the transportation cost for the users of the terminal network, as well as the location cost for the terminal operators. A problem-specific GRASP (greedy randomized adaptive search procedure) is developed to solve the bi-objective terminal location problem efficiently. The algorithm only has a single parameter, that determines the allowed calculation time and can be used to improve the quality of the Pareto set approximation.

Measuring and rewarding flexibility in collaborative distribution, including two-partner coalitions

Horizontal collaboration among shippers is gaining traction as a way to increase logistic efficiency. The total distribution cost of a logistic coalition is generally between 9% and 30% lower than the sum of costs of each partner distributing separately. However, the coalition gain is highly dependent on the flexibility that each partner allows in its delivery terms. Flexible delivery dates, flexible order sizes, order splitting rules, etc., allow the coalition to exploit more opportunities for optimization and create better and cheaper distribution plans. An important challenge in a logistic coalition is the division (or sharing) of the coalition gain. Several methods have been proposed for this purpose, often stemming from the field of game theory. This paper states that an adequate gain sharing method should not only be fair, but should also reward flexibility in order to persuade companies to relax their delivery terms. Methods that limit the criteria for cost allocation to the marginal costs and the values of the sub coalitions are found to be able to generate adequate incentives for companies to adopt a flexible position. In a coalition of two partners however, we show that these methods are not able to correctly evaluate an asymmetric effort to be more flexible. For this situation, we suggest an alternative approach to better measure and reward the value of flexibility.

Analysis of different cost allocation methods in a collaborative transport setting

In collaborative transport, dividing the total cost of the coalition between its different partners is a key issue. However, as each coalition has its own set of preferences and has partners with different characteristics, a cost allocation method suitable in all situations does not exist. In this paper, a set of cost allocation methods, some academic and some used in practice, are evaluated in different situations. We investigate how well these methods behave when partners have different characteristics, e.g., when one partner ships a much larger volume than the others, it is very likely that this partner does not agree to allocate costs according to the volume of each partner. We provide an overview of which cost allocation methods suffice in which situations, showing that a right cost allocation is highly dependent on the characteristics of the coalition.

Gain Sharing in Horizontal Logistic Co-operation: A Case Study in the Fresh Fruit and Vegetables Sector

More and more companies start to notice the potential of setting up a logistic co-operation. They realize however that this idea is also a source of new challenges and impediments. We will focus on the challenge of dividing the total coalition gain among all partners. In this chapter, we show that significant differences exist between allocation methods and we examine the impact of defining gain defining gain sharing on a short term (daily) or a long term (monthly) basis. Too often, the selection of an appropriate allocation mechanism is considered as an independent decision with fairness as the single criterion. The companies involved, however, should realize what the impact of a certain allocation method might be, when applied in the broader context of horizontal co-operation. A selection of well known allocation methods and concepts is introduced and applied to a real life case study of fresh produce traders, jointly organising their transportation from the auction to a joint transport platform.