1,203 research outputs found
The load planning problem for double-stack intermodal trains
Les trains qui transportent des conteneurs empilés (en deux niveaux) sont un élément important
du reseau de transport nord-americain. Le probleme de chargement des wagons correspond un
probleme operationnel d'utilisation rencontre dans les terminaux ferroviaires. Elle consiste
optimiser lâaffectation des conteneurs des emplacements spĂ©cifiques sur les wagons.
Ce mémoire est centré sur un article scientifique traitant le chargement optimal publié dans
le Journal Européen de Recherche Opérationnelle (Volume 267, Numéro 1, Pages 107-119, 2018).
Nous avons formule un modele lineaire en nombres entiers (ILP) et apporte un certain nombre
de contributions. Premierement, nous avons proposé une méthodologie générale qui peut traiter
des wagons double ou simple empilement avec des «patrons» de chargement arbitraires. Les
les patrons tiennent un compte des dépendances de chargement entre les plateformes sur un wagon
donne. Deuxiemement, nous avons modéliser les restrictions du centre de gravité (COG), les
regles dâempilement et un nombre de restrictions techniques de chargement associees certains
types de conteneurs et / ou de marchandises. Les resultats montrent que nous pouvons resoudre
des instances de taille realiste dans un dÂŽelai raisonnable en utilisant un solveur ILP commercial
et nous illustrons que le fait de ne pas tenir compte de la correspondance conteneurs-wagons
ainsi que des restrictions COG peut conduire une surestimation de la capacité disponible.Double-stack trains are an important component of the railroad transport network for containerized cargo in specific markets such as North America. The load planning problem embodies an operational problem commonly faced in rail terminals by operators. It consists in optimizing the assignment of containers to specific locations on the train. The work in this thesis is centered around a scientific paper on the optimization on load planning problem for double stack-trains, published in the European Journal of Operation Research (Volume 267, Issue 1, Pages 1-398) on 16 May 2018. In the paper, we formulated an ILP model and made a number of contributions. First, we proposed a general methodology that can deal with double- or single-stack railcars with arbitrary loading patterns. The patterns account for loading dependencies between the platforms on a given railcar. Second, we modeled Center of gravity (COG) restrictions, stacking rules and a number of technical loading restrictions associated with certain types of containers and/or goods. Results show that we can solve realistic size instances in reasonable time using a commercial ILP solver and we illustrate that failing to account for containers-to-cars matching as well as COG restrictions may lead to an overestimation of the available train capacity
Load sequencing for double-stack trains
Les trains aÌ empilement double sont une composante majeure du reÌseau de transport ferroviaire pour les conteneurs intermodaux dans certains marcheÌs comme celui de lâAmeÌrique du Nord. Le seÌquençage du chargement repreÌsente un probleÌme opeÌrationnel auquel font face les opeÌrateurs de grues dans les cours de chargement lorsquâils ont pour taÌche de placer les conteneurs sur un train. Le seÌquençage du chargement consiste aÌ trouver une seÌquence de mouvements permettant dâextraire les conteneurs des piles dans lesquels ils sont entreposeÌs afin de les placer sur le train. Le seÌquençage du chargement est interrelieÌ avec la planification du chargement, processus dans lequel des conteneurs sont assigneÌs aÌ des placements speÌcifiques sur les wagons, afin de former un plan de chargement pour guider le seÌquençage.
Le travail dans ce meÌmoire sâarticule autour dâun article scientifique sur lâoptimisation du seÌquençage du chargement pour les trains aÌ empilement double. Dans cet article sont preÌsenteÌs des algorithmes baseÌs sur la programmation dynamique, ainsi quâune strateÌgie tirant avantage de plans de chargement deÌveloppeÌs afin de solutionner le seÌquençage pour des instances de chargement reÌalistes. Les reÌsultats montrent que les heuristiques suggeÌreÌes fonctionnent bien meÌme pour des instances de grande taille. Ces dernieÌres preÌsentent une leÌgeÌre perte en qualiteÌ des solutions mais un temps dâexeÌcution nettement infeÌrieur aux meÌthodes exactes faisant deÌfaut pour des instances de grande taille. Lâanalyse deÌmontre eÌgalement que lâutilisation de plans de chargement plus flexibles permet dâameÌliorer la qualiteÌ des solutions avec toutes les meÌthodes, ceci se faisant au couÌt dâun temps dâeÌxecution supeÌrieur et lâabsence dâune garantie de solution pour les heuristiques. Finalement, la planification et le seÌquençage simultaneÌ sont compareÌs avec lâapproche successive utilisant les algorithmes developpeÌs afin dâeÌvaluer la performance relative des deux approches.Double-stack trains are an important component of the railroad transport network for containerized cargo in specific markets such as the North American one. The load sequencing is an operational problem commonly faced in rail terminals by crane operators when tasked with loading containers on the railcars of a train. The load sequencing problem aims to find an efficient sequence of container retrievals in the storage yard, where containers are stored in piles while awaiting departure by train. Load sequencing is interrelated with load planning, the assignment of containers to specific locations on the train, forming a load plan which guides the load sequencing.
The work in this thesis is centered around a scientific paper on the optimization of load sequencing for double-stack trains. This paper proposes algorithms based on dynamic programming and a strategy leveraging the load plans, and assesses their performance in terms of computing time, tractability and solution quality on realistic instance sizes. The results show that the heuristics suggested to solve the load sequencing scale well for realistic instance size, managing to achieve a significantly reduced computing time with a small loss in solution quality compared to exact methods, which would often falter for larger instances. The analysis also illustrates how using a flexible load plan in the load sequencing significantly improves solution quality at the cost of greater computing requirements and lack of guaranteed solution for the heuristics. Finally, the paper compares the performance resulting from the successive application of load planning and sequencing with jointly performing the load planning and sequencing
Integrated Scheduling of Vessels, Cranes and Trains to Minimize Delays in a Seaport Container Terminal
The multiple processes taking place on a daily basis at an intermodal container terminal are often considered individually, given the complexity of their joint consideration. Nevertheless, the integrated planning and scheduling of operations in an intermodal terminal, including the arrivals and departures of trains and vessels, is a very relevant topic for terminal managers, which can benefit from the application of Operations Research (OR) techniques to obtain near-optimal solutions without excessive computational cost. Applying the functional integration technique, we present here a mathematical model for this terminal planning process, and solve it using heuristic procedures, given its complexity and size. Details on the benchmark comparison of a genetic algorithm, a simulated annealing routine and a tabu search are provided for different problem instances
Tactical block planning for intermodal rail transportation
Le mĂ©moire prĂ©sente le problĂšme de la planification tactique des âblocksâ pour le transport ferroviaire intermodal, qui a Ă©tĂ© peu Ă©tudiĂ© jusquâĂ prĂ©sent. Nous proposons un nouveau modĂšle de design de rĂ©seau en tenant compte de la spĂ©cificitĂ© du transport intermodal. La recherche se concentre sur le contexte nord-amĂ©ricain et fait suite Ă une Ă©troite collaboration
avec lâune des principales compagnies ferroviaires nord-amĂ©ricaines.
Le âblockingâ constitue une importante opĂ©ration de transport ferroviaire de marchandises, par laquelle des wagons dâorigines et de destinations potentiellement diffĂ©rentes sont regroupĂ©s pour ĂȘtre dÂŽeplacĂ©s et manipulĂ©s comme une seule unitĂ©, ce qui permet des Ă©conomies dâĂ©chelle. La littĂ©rature se limite aux travaux traitant le problĂšme classique du blocage des trains, oĂč la demande est exprimĂ©e en termes de wagons. A notre connaissance, aucun travail prĂ©alable nâa Ă©tĂ© consacrĂš Ă un contexte de transport intermodal, oĂč la demande est exprimĂ©e en termes de conteneurs Ă dĂšplacer dâun terminal dâorigine donnĂ© vers un terminal de destination donnĂ©, introduisant ainsi un processus de consolidation supplĂ©mentaire.
Nous proposons un modĂšle de âblockingâ qui prend en compte plusieurs types de conteneurs et wagons, intĂ©grant lâaffectation conteneur-wagon. Nous prĂ©sentons un nouveau modĂšle de design de rĂ©seau Ă trois couches en temps continu formulĂ© sous la forme dâun programme linĂ©aire mixte en nombres entiers (MILP), dans le but de minimiser le coĂ»t total de transport composĂ© par la sĂ©lection de blocs, les coĂ»ts dâexploitation et la gestion du coĂ»t de la demande. Le modĂšle peut ĂȘtre rĂ©solu en utilisant un solveur commercial pour des tailles rĂ©alistes. Nous illustrons les performances et lâintĂ©rĂȘt de la mĂ©thode proposĂ©e Ă travers une Ă©tude de cas approfondie dâun important chemin de fer nord-amĂ©ricain.The thesis presents the tactical block-planning problem for intermodal railroads, which has been little studied so far. We propose a new block service network design model considering the specificity of intermodal rail. The research focuses on the North American context and follows a close collaboration with one of the major North American railroad companies.
Blocking constitutes an important rail freight transport operation, by which cars with potentially different origins and destinations are grouped to be moved and handled as a single unit, yielding economies of scale. The literature is limited to works addressing the classical train blocking problem, where demand is given in terms of cars to be blocked among
specific OD pairs. To the best of our knowledge, no prior work has been dedicated to an intermodal transportation context, where demand is expressed in terms of containers to be moved from a given origin terminal to a given destination terminal, hence introducing an additional consolidation process.
We propose a blocking model that considers several types of containers and railcars, integrating the container-to-car assignment. We present a new continuous-time, three-layer service network design model formulated as a Mixed Integer Linear Program (MILP), with the objective of minimizing the total transportation cost composed by block selection, operation costs, and handling demand cost. The model can be solved using commercial solver for realistic sizes. We illustrate the performance and interest of the proposed method through an extensive case study of a major North American railroad
New solution approaches for the Train Load Planning Problem
The present paper faces the train load planning problem in container
terminals. The problem consists of assigning containers to rail wagons while maximizing the total priority of the containers loaded and minimizing the number of
rehandles executed in the terminal yard. Two diferent heuristic approaches, based
on an innovative way to compute weight limitations and on two 0/1 integer programming models, are proposed and compared on the basis of specifc key performance
indicators. The heuristic approaches are compared using random generated instances
based on real-world data. An extensive computational analysis has been performed
Development of a multimodal port freight transportation model for estimating container throughput
Computer based simulation models have often been used to study the multimodal freight transportation system. But these studies have not been able to dynamically couple the various modes into one model; therefore, they are limited in their ability to inform on dynamic system level interactions. This research thesis is motivated by the need to dynamically couple the multimodal freight transportation system to operate at multiple spatial and temporal scales. It is part of a larger research program to develop a systems modeling framework applicable to freight transportation. This larger research program attempts to dynamically couple railroad, seaport, and highway freight transportation models. The focus of this thesis is the development of the coupled railroad and seaport models. A separate volume (Wall 2010) on the development of the highway model has been completed.
The model railroad and seaport was developed using ArenaÂź simulation software and it comprises of the Ports of Savannah, GA, Charleston, NC, Jacksonville, FL, their adjacent CSX rail terminal, and connecting CSX railroads in the southeastern U.S. However, only the simulation outputs for the Port of Savannah are discussed in this paper. It should be mentioned that the modeled port layout is only conceptual; therefore, any inferences drawn from the model's outputs do not represent actual port performance.
The model was run for 26 continuous simulation days, generating 141 containership calls, 147 highway truck deliveries of containers, 900 trains, and a throughput of 28,738 containers at the Port of Savannah, GA. An analysis of each train's trajectory from origin to destination shows that trains spend between 24 - 67 percent of their travel time idle on the tracks waiting for permission to move. Train parking demand analysis on the adjacent shunting area at the multimodal terminal seems to indicate that there aren't enough containers coming from the port because the demand is due to only trains waiting to load. The simulation also shows that on average it takes containerships calling at the Port of Savannah about 3.2 days to find an available dock to berth and unload containers. The observed mean turnaround time for containerships was 4.5 days.
This experiment also shows that container residence time within the port and adjacent multimodal rail terminal varies widely. Residence times within the port range from about 0.2 hours to 9 hours with a mean of 1 hour. The average residence time inside the rail terminal is about 20 minutes but observations varied from as little as 2 minutes to a high of 2.5 hours. In addition, about 85 percent of container residence time in the port is spent idle.
This research thesis demonstrates that it is possible to dynamically couple the different sub-models of the multimodal freight transportation system. However, there are challenges that need to be addressed by future research. The principal challenge is the development of a more efficient train movement algorithm that can incorporate the actual Direct Traffic Control (DTC) and / or Automatic Block Signal (ABS) track segmentation. Such an algorithm would likely improve the capacity estimates of the railroad network. In addition, future research should seek to reduce the high computational cost imposed by a discrete process modeling methodology and the adoption of single container resolution level for terminal operations. A methodology combining both discrete and continuous process modeling as proposed in this study could lessen computational costs and lower computer system requirements at a cost of some of the feedback capabilities of the model This tradeoff must be carefully examined.M.S.Committee Chair: Rodgers, Michael; Committee Member: Guensler, Randall; Committee Member: Hunter, Michae
Regulating privatized rail transport
Traditionally, transport regulation has been viewed as an exercise in second-best optimization, acknowledging the existence of huge information problems. Then the rail industry was deeply restructured worldwide to halt erosion of the sector's share of transportation markets. Restructuring took different forms in different countries, ranging from simple reorganization measures to extreme restructuring -with the private sector increasingly participating in the sector and with the provision of infrastructure separated from the provision of services. The authors argue that regulation of the rail industry cannot remain unaffected by these changes. New regulatory scenarios and issues have emerged. For example, contracts have to be defined for private participation and quality surveillance instruments must be defined. Traditional price controls have to be adapted to, and mechanisms designed to manage and plan infrastructure investments in, the new environment. Restructuring has brought new problems, too. Where licenses have been used, for example, several concessionaires have been unable to meet the objectives spelled out in the concession contract. Contracts should be flexible enough to take account of novel situations that may affect company performance. And yet, for the system to be credible, there cannot be systematic, unjustified deviations from the franchise objectives. Regulation of the sector should be simple and flexible, with license contracts designed to include the private sector and with industry organization adapted to local circumstances. Regulation should be governed by principles that foster competition and market mechanisms, wherever possible. At the same time, it should provide a stable legal and institutional framework for economic activity. Otherwise, regulators should refrain from intervening in the market-unless the goal of economic efficiency (subject to the socially demanded levelof equity) is in jeopardy.Municipal Financial Management,Banks&Banking Reform,Decentralization,Enterprise Development&Reform,Public Sector Economics&Finance,Railways Transport,Banks&Banking Reform,Municipal Financial Management,Water and Industry,Public Sector Economics&Finance
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