The school bus routing problem: An analysis and algorithm

In this paper we analyse a flexible real world-based model for designing school bus transit systems and note a number of parallels between this and other well-known combinatorial optimisation problems including the vehicle routing problem, the set covering problem, and one-dimensional bin packing. We then describe an iterated local search algorithm for this problem and demonstrate the sort of solutions that we can expect with different types of problem instance

Low Level Waste Conceptual Design Adaption to Poor Geological Conditions

Since the early eighties, several studies have been carried out in Belgium with respect to a repository for the final disposal of low-level radioactive waste (LLW). In 1998, the Belgian Government decided to restrict future investigations to the four existing nuclear sites in Belgium or sites that might show interest. So far, only two existing nuclear sites have been thoroughly investigated from a geological and hydrogeological point of view. These sites are located in the North-East (Mol-Dessel) and in the mid part (Fleurus-Farciennes) of the country. Both sites have the disadvantage of presenting poor geological and hydrogeological conditions, which are rather unfavorable to accommodate a surface disposal facility for LLW. The underground of the Mol-Dessel site consists of neogene sand layers of about 180 m thick which cover a 100 meters thick clay layer. These neogene sands contain, at 20 m depth, a thin clayey layer. The groundwater level is quite close to the surface (0-2m) and finally, the topography is almost totally flat. The upper layer of the Fleurus-Farciennes site consists of 10 m silt with poor geomechanical characteristics, overlying sands (only a few meters thick) and Westphalian shales between 15 and 20 m depth. The Westphalian shales are tectonized and strongly weathered. In the past, coal seams were mined out. This activity induced locally important surface subsidence. For both nuclear sites that were investigated, a conceptual design was made that could allow any unfavorable geological or hydrogeological conditions of the site to be overcome. In Fleurus-Farciennes, for instance, the proposed conceptual design of the repository is quite original. It is composed of a shallow, buried concrete cylinder, surrounded by an accessible concrete ring, which allows permanent inspection and control during the whole lifetime of the repository. Stability and drainage systems should be independent of potential differential settlements an d subsidences. Potential radionuclides releases are controlled and have a single discharge point to the biosphere

Borehole seismic profiling and tube wave applications in a dam site investigation

Continuous, single-channel reflection profiling has been carried out in PVC-lined boreholes, primarily with the aim of ascertaining the position of an old subsurface gas storage tunnel on a proposed dam site.Tube wave reflection patterns thus generated have been interpreted in terms of sediment rigidity and shear wave velocity, and these results could be compared with some independent data. It is interesting to note that, within the well section penetrating Tertiary clays, the velocity of the hydraulic transients apparently was not affected by the PVC casing, which might be explained by a tight coupling between casing and clay wall. In such situations, tube waves turn out a straightforward tool for the determination of shear wave velocity and the derivation of dynamic elastic moduli of unconsolidated sediments.Further applications of the study of the distribution of seismic velocities on the dam site dealt with the consolidation history of the clays. A level of abnormally low P-wave velocities has been detected and interpreted as a gas-charged horizon which, by its coincidence with the base level of clay diapirs, might be considered to have contributed to clay flowage in past geological times. Data about maximum past burial depth, derived from shear wave velocities, turned out to be in agreement with results from consolidation testing

A metaheuristic for the school bus routing problem with bus stop selection

Existing literature on routing of school buses has focused mainly on building intricate models that attempt to capture as many real-life constraints and objectives as possible.In contrast,the focus of this paper is on understanding the joint problem of bus route generation and bus stop selection –two important sub-problems – in its most basic form.To this end,this paper defines the school bus routing problem (SBRP) as a variant of the vehicle routing problem in which three simultaneous decisions have to be made :(1)determine the set of stops to visit,(2)determine for each student which stop (s)he should walk to, and (3)determine routes that lie along the chosen stops,so that the total traveled distance is minimized. An MIP model of this basic problem is developed. To increase the practical usefulness and to solve large instances of the SBRP,an efficientparameter-free GRASP + VND meta heuristic is developed.This method is a matheuristic since it uses an exact algorithm to optimally solve the sub-problem of assigning students to stops when routes are given.The results of this matheuristic approach on 112 artificially generated instances are compared to solutions found by a sequential method, to solutions obtained by implementing a MIP model in a commercial solver,and to a lower bound obtained by a dedicated column generation approach.Using appropriate statistical techniques ,a neighborhood analysis is performed to test the design of the metaheuristic.Similarly,the characteristics of the problem instance that determine the computing time of the metaheuristic are discovered using statistical analysis.Finally,the importance of integrating all decisions in a single model is shown experimentally by comparing the metaheuristic to a sequential method. Experiments show that the matheuris tic exhibits excellent performance and finds optimal or close-to-optimal solutions of large instances of the SBRP in very limited computing times.publisher: Elsevier articletitle: A metaheuristic for the school bus routing problem with bus stop selection journaltitle: European Journal of Operational Research articlelink: http://dx.doi.org/10.1016/j.ejor.2013.02.025 content_type: article copyright: Copyright © 2013 Elsevier B.V. All rights reserved.status: publishe

Can a holistic optimization improve SESAR Key Performance Areas?

There is a need to cope with the expected growth in air traffic while simultaneously meeting demands for increased safety, predictability, and efficiency in air traffic management (ATM) systems. This paper explores the potential effects of a holistic optimization approach on performance of air traffic management systems. We developed and evaluated a tool for optimizing the decision-making process of airport ATM based on holistic optimization, i.e., optimization where each decision is based on all possible airplane movements at the airport. This paper describes the results of a case study investigating the usefulness of this optimization approach. Our results indicate that active operational use of holistic decisions based on optimization tools might reduce taxi time and improve punctuality. Such tools can improve decision making in air traffic control (ATC) towers and contribute to the improvement of the overall ATC process