A Granular Variable Tabu Neighborhood Search for the capacitated location-routing problem

This paper proposes a new heuristic algorithm for the Capacitated Location-Routing Problem (CLRP), called Granular Variable Tabu Neighborhood Search (GVTNS). This heuristic includes a Granular Tabu Search within a Variable Neighborhood Search algorithm. The proposed algorithm is experimentally compared on the benchmark instances from the literature with several of the most effective heuristics proposed for the solution of the CLRP, by taking into account the CPU time and the quality of the solutions obtained. The computational results show that GVTNS is able to obtain good average solutions in short CPU times, and to improve five best known solutions from the literature. The main contribution of this paper is to show a successful new heuristic for the CLRP, combining two known heuristic approaches to improve the global performance of the proposed algorithm for what concerns both the quality of the solutions and the computing times required to find them.     

A ‘Less-flexibility-first’ Heuristic for the Placement of Inland Vessels in a Lock

Abstract

Inland vessels move goods along waterways (canals and rivers) and they visit ports. Because of their tidal nature, vessels make use of locks to enter ports or waterways. From a port management point of view, fast access to and from the port and high utilization of locks are important objectives. Where the former relates to low inbound and outbound waiting times, the latter relates to the placement of as many vessels as possible in the lock before its operation. This article includes a case study that relates to the operation of the Van Cauwelaert lock in the port of Antwerp, Belgium. Lock operation policy is as follows: vessels wait in front of the lock for a port administrator to assign places in the lock based on knowledge of the vessels’ dimensions. As such, there is no FIFO-discipline, but a ‘group-FIFO’-discipline, i.e. if n vessels are allowed into the lock, they are the first n vessels in the arrival queue. A heuristic algorithm is formulated for the placement of vessels in the lock. This algorithm supports the decision where to place the vessel in the lock, aiming to place as many vessels as possible from the arrival queue. At the same time, it supports the decision to start a locking operation or not, based on information about vessels that are announced but which have not yet arrived at the lock's entrance. The heuristic is called a ‘less-flexibility-first’-heuristic as it looks for pseudo-placements, showing which flexibility is left for the remaining vessels after placing a vessel. This article describes the implementation of the heuristic and provides numerical examples. A comparison is made between the heuristic results and daily practice, based on real-life vessel movements through the Van Cauwelaert lock in 2002.     

What Does Happen to Our Driving When We Get Older?

Abstract

The objective of this paper is to uncover the main antecedents associated with driving errors among older drivers in order to establish a framework for analyzing potential skill improvements using other approaches, for example, games. The article also aims at classifying age-related declines in seniors' abilities associated with their driving performance. The research undertakes an analysis of attempts made through the investigation of the literature. We have systematically searched papers and extracted (1) prevalent driving errors among seniors and (2) underlying age-related declines in seniors' abilities associated with their driving performance. We have also identified some characteristics of the research in this area (e.g. the research methods and geographical distribution of the research). Our expert panel mapped the functional declines in seniors' abilities to the driving errors to identify the relationship between these findings. A reliability test resulted in 81% reliability of findings. We have identified eight groups of driving errors, which could be affected by physical, visual, and cognitive declines among seniors. According to the experts' opinions, the underlying relationship of physical, visual, and cognitive declines among seniors and their driving errors were also presented. Our findings show that there is a potential for the use of innovative interventions such as playing video games to create an inexpensive, motivational, and enjoyable method that may provide a transfer effect to specific driving skills. This could help improve seniors' driving performance by improving specific functional abilities associated with driving.     

Optimum Capacity for Intermodal Container Terminals

Abstract

Achievement of a desirable level of customer service at intermodal terminals mainly depends on the efficient loading and unloading of trains without delays. The efficiency of the transfer between the modes in the terminal area can have a significant effect on these delays. In this article, an analytically based simulation model is developed to investigate delays of trains for different service configurations. Simulation outputs are used to find an optimum balance of the cost of train delays and variation from the desired level of service. Data from the Acacia Ridge Terminal in Brisbane, Australia are used to validate and test the model.     

Heuristic approach to the airline schedule disturbances problem

Abstract

When disturbances make it impossible to realise the planned flight schedule, the dispatcher at the airline operational centre defines a new flight schedule based on airline policy, in order to reduce the negative effects of these perturbations. Depending on airline policy, when designing the new flight schedule, the dispatcher delays or cancels some flights and reassigns some flights to available aircraft. In this paper, a decision support system (DSS) for solving the airline schedule disturbances problem is developed aiming to assist decision makers in handling disturbances in real-time. The system is based on a heuristic algorithm, which generates a list of different feasible schedules ordered according to the value of an objective function. The dispatcher can thus select and implement one of them. In this paper, the possibilities of DSS are illustrated by real numerical examples that concern JAT Airways' flight schedule disturbances.     

A distributed origin–destination demand estimation approach for real-time traffic network management

Abstract

This paper describes a distributed recursive heuristic approach for the origin–destination demand estimation problem for real-time traffic network management applications. The distributed nature of the heuristic enables its parallelization and hence reduces significantly its processing time. Furthermore, the heuristic reduces dependency on historical data that are typically used to map the observed link flows to their corresponding origin–destination pairs. In addition, the heuristic allows the incorporation of any available partial information on the demand distribution in the study area to improve the overall estimation accuracy. The heuristic is implemented following a hierarchal multi-threading mechanism. Dividing the study area into a set of subareas, the demand of every two adjacent subareas is merged in a separate thread. The merging operations continue until the demand for the entire study area is estimated. Experiments are conducted to examine the performance of the heuristic using hypothetical and real networks. The obtained results illustrate that the heuristic can achieve reasonable demand estimation accuracy while maintaining superiority in terms of processing time.     

Transport and nation‐state governments worldwide

The Sydney Olympics held in September 2000 provided an opportunity to monitor the planning of transport provision for the world's greatest sporting spectacular. As the single largest major event, the pressures on a city's transport system are enormous, as witnessed by the previous Games in Atlanta and Barcelona. This paper takes a value-chain approach to assess transport performance as a crucial element in the delivery of the Sydney Olympic Games. We begin with a brief overview of strategic value, highlighting some generic aspects of value chains followed by the transport delivery system that came to the fore as significant 'drivers' in the value chain. This is followed by a summary of the effectiveness of the buses, trains, taxis, roads and the airport. A more detailed look is provided of the private bus sector where the problems leading up the opening of the Games received a great deal of media attention. The paper concludes with two stories, one good, one not so good, about transport and the Olympic Games.     

Computing 4D near-optimal trajectories for dynamic air traffic flow management with column generation and branch-and-price

Abstract

The current air traffic system faces recurrent saturation problems. Numerous studies are dedicated to this issue, including the present research on a new dynamic regulation filter holding frequent trajectory optimisations in a real-time sliding horizon loop process. We consider a trajectory optimisation problem arising in this context, where a feasible four-dimensional (4D) trajectory is to be built and assigned to each regulated flight to suppress sector overloads while minimising the cost of the chosen policy. We model this problem with a mixed integer linear programme and solve it with a branch-and-price approach. The pricing sub-problem looks for feasible trajectories in a dynamic three-dimensional (3D) network and is solved with a specific algorithm based on shortest path labelling algorithms and on dynamic programming. Each algorithm is tested on real-world data corresponding to a complete traffic day in the European air traffic system; experimental results, including computing times measurement, validate the solution process.     

A Heuristic Algorithm for the Allocation of Airport Runway System Capacity

Abstract

This paper develops a heuristic algorithm for the allocation of airport runway capacity to minimise the cost of arrival and departure aircraft/flight delays. The algorithm is developed as a potential alternative to optimisation models based on linear and integer programming. The algorithm is based on heuristic (‘greedy’) criteria that closely reflect the ‘rules of thumb’ used by air traffic controllers. Using inputs such as arrival and departure demand, airport runway system capacity envelopes and cost of aircraft/flight delays, the main output minimises the cost of arrival and departure delays as well as the corresponding interdependent airport runway system arrival and departure capacity allocation. The algorithm is applied to traffic scenarios at three busy US airports. The results are used to validate the performance of the proposed heuristic algorithm against results from selected benchmarking optimisation models.     

Liner shipping network design with emission control areas: A genetic algorithm-based approach

To curb emissions, containerized shipping lines face the traditional trade-off between cost and emissions (CO₂ and SO_x) reduction. This paper considers this element in the context of liner service design and proposes a mixed integer linear programming (MILP) model based on a multi-commodity pickup and delivery arc-flow formulation. The objective is to maximize the profit by selecting the ports to be visited, the sequence of port visit, the cargo flows between ports, as well as the number/operating speeds of vessels on each arc of the selected route. The problem also considers that Emission Control Areas (ECAs) exist in the liner network and accounts for the vessel carrying capacity. In addition to using the MILP solver of CPLEX, we develop in the paper a specific genetic algorithm (GA) based heuristic and show that it gives the possibility to reach an optimal solution when solving large size instances.     

Optimal shipment decisions for an airfreight forwarder: Formulation and solution methods

We study the freight forwarder’s shipment planning problem in an airfreight forwarding network where a set of cargo shipments have to be transported to given destinations. We provide mixed integer programming formulations that use piecewise-linear cargo rates and account for volume and weight constraints, flight departure/arrival times, as well as shipment-ready times.After exploring the solution of such models using CPLEX, we devise two solution methodologies to handle large problem sizes. The first is based on Lagrangian relaxation, where the problems decompose into a set of knapsack problems and a set of network flow problems. The second is a local branching heuristic that combines branching ideas and local search. The two approaches show promising results in providing good quality heuristic solutions within reasonable computational times, for difficult and large shipment consolidation problems.     

Some thoughts on competitive tendering in local bus operations

Abstract

This article is derived from a report by Metra Consulting Group for the Dutch Ministry of Public Health and the Environment. The aim of Metra's study was to identify ways of reducing the environmental nuisance of urban traffic without adding excessively to transport costs.

The main theme of the article is that the traditional idea of an inherent conflict between transport efficiency and the environment is mistaken. Both efficiency and the environment are threatened by the same thing: the excessive and indiscriminate use of vehicles. This comes about because of defects in the fiscal and regulatory framework within which people take transport decisions. Suitable reforms in this framework would simultaneously enhance the environment and improve access for all classes of road user.

In the development of this theme, particular attention is paid to transport activities which tend to be neglected by policy makers, such as walking, cycling and urban goods distribution; and to measures which are not always thought of as instruments of policy at all, such as locational policy and development control, vehicle design, and vehicle taxation, especially of goods vehicles.     

Determining the effects of scheduling on automated automobile guideway utilization

This paper develops an analytic approach for measuring the effect of vehicle scheduling and of metering methods required to balance entrance rates among stations on lane capacity utilization of automated automobile guideways. The scheduling process at each entrance is represented by a probabilistic model which generates a system of nonlinear equations. The solution of this system yields the maximum steady state input rates at the entrances to the guideway system. The method developed is applicable to network configurations in which a small number of merges must be scheduled for each vehicle before it enters the guideway. It is demonstrated by application to a corridor guideway serving a major activity center during peak inbound demand, and also it is shown how the approach may be extended to more complex networks.     

Fundamentals of discrete multimodal choice modelling

Abstract

In this paper an overview is given of the most relevant issues relating to the application of multimodal choice models, with particular emphasis on disaggregate modal split models. The paper considers questions of data, such as type of data, alternative sampling strategies and problems of measurement; and modelling issues, such as model specification and estimation, including a good presentation of the statistical techniques'available. The paper also addresses the aggregation problem, which lies at the heart of one of today's most hotly contested debates: whether to use aggregate or disaggregate models for policy analysis, and in which circumstances.     

Assigning fighter plane formations to enemy aircraft using fuzzy logic

Fighter aircraft protect specific facilities on alert in the air by patrolling expectation zones. These zones are located in the direction from which enemy aircraft attacks are expected; fighter formations are sent from them to intercept enemy aircraft. The problem considered in this paper is to determine the optimum assignment of fighter plane formations to enemy formations. The proposed solution is based on fuzzy logic and integer linear programming. A numerical example is given to illustrate the application possibilities of the proposed solution.     

Synchronized Production and Transportation Planning Using Subcontracted Vehicles in a Production-Distribution Network

Abstract

Effective management of interfaces between procurement, supply, production and distribution for higher efficiency in the supply chain is an important issue in global manufacturing, where the synchronization of production and transportation planning represents important savings in operational costs. This paper focuses on the synchronization of production planning and transportation planning in a production distribution network, where transportation is subcontracted to a professional transportation enterprise (PTE) for vehicle-hiring. Dynamic and flexible numbers of vehicles are used to cater for fast changing market demands. Thus, the number of vehicles to be hired is viewed from the planning point of view as an operational decision considered simultaneously with production and transportation planning. A mathematical model – SPTP/MTDS – for synchronized production and transportation planning under multiple times and direct shipping strategy (MTDS) is discussed, and a Lagrange relaxation decomposition-based two layer decision procedure (LRD-TLDP) is developed. By introducing artificial decision variables and Lagrange multipliers, SPTP/MTDS is decomposed into a production decision sub-problem (SPTP-PD), and a distribution decision sub-problem (SPTP-DD). A priority-based assignment heuristic and a partial chain-based genetic algorithm are developed to solve SPTP-PD and SPTP-DD, respectively. An illustration of the application of the model in an electronic appliance manufacturing enterprise in China is presented.     

Port privatization policy and practice

In recent years a significant number of countries have implemented policies aimed at reforming their port industry. In the belief that it will improve efficiency and reduce the heavy financial burden placed upon governments that attempt to support such a capital-intensive industry, privatization has often formed an important strand of such policies. A key claim in favour of privatization is that the transfer of ownership from public to private hands will ultimately lead to an improvement in economic efficiency and, hence, financial and operational performance. This paper investigates the theoretical underpinnings and practical validity of this claim and concludes that privatization is only a partial cure for what ails the world's ports and that, if implemented in isolation, it simply cannot deliver the much-needed panacea for the industry's woes.     

Acquisition,efficiency and scale economies: An analysis of the British bus industry

The British Bus industry has undergone considerable transformation since privatization. Five major operators have emerged to dominate the market, a position almost exclusively attained through acquisition. This paper reviews the economies of scale argument commonly cited for this change and gives an overview of the acquisition process. It questions whether this argument gives a complete explanation for this industry development. For 58 individual companies, the level of technical efficiency attributable to firms operating at or near the optimum level of output is examined over 5 years to determine if mergers in practice have resulted in scale economies. Technical efficiency is estimated using data envelopment analysis, under assumptions of constant and variable returns to scale. Efficiency scores are then regressed on a time trend and a merger dummy to test whether acquired firms' efficiency has significantly improved above the average. It was found that over the period, efficiency had improved. This improvement, however, cannot be wholly attributed to the achievement of economies of scale. More specifically, there has been an improvement in the internal efficiency of acquired firms and some scale economies within group companies, the latter of which may have resulted from the eradication of competition.     

A solution algorithm for a dynamic deterministic user equilibrium assignment model with departure time choice

Abstract

A route-based combined model of dynamic deterministic route and departure time choice and a solution method for many origin and destination pairs is proposed. The divided linear travel time model is used to calculate the link travel time and to describe the propagation of flow over time. For the calculation of route travel times, the predictive ideal route travel time concept is adopted. Solving the combined model of dynamic deterministic route and departure time choice is shown to be equivalent to solving simultaneously a system of non-linear equations. A Newton-type iterative scheme is proposed to solve this problem. The performance of the proposed solution method is demonstrated using a version of the Sioux Falls network. This shows that the proposed solution method produces good equilibrium solutions with reasonable computational cost.     

Airline scheduling: a heurisitic approach

In this paper a practical technique for finding improved airline routings and schedules is developed. A dynamic programming algorithm is combined with a heuristic method for assigning routes to the aircraft such that the expected total contribution to profit is maximum. Expected passenger demands and priorities are taken to be an input to the model. The model may be used to check the effect on the total system of adding or removing aircraft or of varying aircraft capacity. Although the test runs were made on data for a six city‐ten aircraft array a smaller, more simple numerical example is given to demonstrate the model logic.