1,029 research outputs found
A heuristic solution for the yearly capacity of an intermodal terminal
No full textThe efficiency of an intermodal terminal is especially measured in terms of time waste for both traffic feeders and loading units (known as intermodal transport units, ITUs) from the moment they arrive at the terminal up to the leaving instant. This makes significant the estimation of the maximum traffic (normally referred to as “capacity”) which allows the terminal to work without loss of efficiency and congestion. The amount of the factors from which capacity depends and their nature (the most of them are stochastic processes with a huge grade of indeterminacy—e.g. traffic peaks, economical fluctuations, delays and so on) make the issue challenging and seldom addressed from scientific literature. This paper deals with a heuristic model for the estimation of the yearly capacity of an intermodal terminal and is organised as follows. General definitions and a wide dissertation on the complexity of the concept may be found in the Section 1, also briefly summarizing some interesting results of the scientific literature. Section 2 describes the model and the assumptions on which it is based. A mathematical formulation of the described problem is contained in the Section 3. The solution method is widely described in the Section 4 and used in the Section 5 for the capacity estimation of one of the most important Italian terminals (two more examples can be found in Appendix A). An evaluation of the achieved results is drawn in the final section sf the paper
Deriving Convergence of Vehicle Routing Problems using a Fictitious Play approach
No full textVehicle Routing Problem (VRP) has been the subject of many studies during the last few years. Many different kinds of algorithms were developed for its solution, as reviewed in Cordeau et al. (2004).
This paper defines VRP as a fictitious play to give mathematical support to the effectiveness of some of the most known solution strategies and techniques. It will be proved that reaching a solution of given requirements is possible in the trivial case (i.e., if the algorithm starts with a solution having the same order of precision), or if the distance between the starting and the final solution can be reduced slightly fast.
After having defined VRP as a fictitious play (paragraph 1), this paper states the well-known theorem of Monderer and Shapley for fictitious plays (paragraph 2). The structure of some of the most recent algorithms for the solution of VRP is then re-examined in the light of this theorem, used as a convergence criterion (paragraph 3). Some conclusions and possibilities of further development are briefly drawn in the final paragraph 4
Externalities and External Costs in Transport Planning
No full textThe concept of “externality” is adopted broadly within the transport literature. By definition, an externality arises when the actions of a subject have an impact on one or more other subjects, and when such impact is not (fully) compensated for by the first subject. This chapter dwells upon the main externalities (including the positive ones) in transport, upon their effects and briefly, upon the methods that can be used to estimate their economic impact
Terminalkapazität im kombinierten Verkehr
No full textDiese Arbeit befasst sich mit dem komplexen Thema der jährlichen Kapazität eines Terminals. Ziel ist es, dieses Problem in seiner Vollständigkeit zu beschreiben und eine heuristische und anwendbare Methode zu finden, die für die größtmögliche Anzahl der Terminals zu einer realistischen Prognose der Kapazität führen kann. Abschnitt 1 enthält einige einleitende Überlegungen.
Das Problem der Terminalkapazität wurde in Abschnitt 2 von einem mathematischen Standpunkt betrachtet. Die Lösungsmethode wird in Abschnitt 3 vorgestellt und in Abschnitt 4 auf zwei italienische Terminals angewendet. Eine Bewertung des erzielten Ergebnisses und die Vorstellung von Weiterentwicklungsmöglichkeiten schließen in Abschnitt 5 die Arbeit ab
Un approccio operativo per la valutazione della qualità nei servizi di trasporto pubblico/An Operational Approach for Quality Evaluation in Public Transport Services
No full textLa valutazione della qualità è una fra le questioni chiave
dell’ingegneria dei trasporti: la rappresentazione attraverso
una serie di relazioni tra velocità e tasso di saturazione
del flusso (così come descritto nel “Manuale di Capacità
delle Strade”) è molto ben conosciuta e largamente
accettata in tutto il mondo, ma riguarda in modo specifico
il trasporto privato. La questione appare più complessa
quando si considera il trasporto pubblico: in questo caso,
la scelta dei parametri influenti e la loro percezione dipendono
in larga misura da impressioni soggettive.
Il metodo presentato in questa memoria considera la
valutazione del trasporto pubblico identificando un gruppo
di fattori che la influenzano e definendo per ciascuno
di essi delle soglie per la valutazione del loro rendimento.
La comprensione e l’applicazione di questa tecnica dovrebbero
risultare alquanto facili e permettere velocemente
l’identificazione delle possibili carenze, garantendo alla
pianificazione dei trasporti uno strumento efficace per l’analisi
ed il miglioramento dei servizi di trasporto pubblico.
The evaluation of Transport Quality is one of the key
issues within Transportation Engineering: as far as motorised
individual transport is concerned, the method of
expressing it through a series of relations between speed
and saturation flow rate (as in the Highway Capacity
Manual) is very well-known and mostly accepted throughout
the world. The matter is more complicated when public
transport (or: transit) is at-stake, as the choice of the
influent parameters and their perception are normally extremely
dependent from subjective impressions.
The method presented in this paper evaluates public
transport identifying a group of influencing factors and
defining for each of them thresholds for the assessment of
their performances. The comprehension and application
of this approach should be easy tasks and allow the fastest
recognition of possible deficiencies, providing transportation
planning with an effective tool for the analysis and
the improvement of transit services
Solving Vehicle Routing Problems using an engineering solution
No full textVehicle Routing Problems (VRPs) have received a lot of attention in the recent years, both from a theoretical and practical perspective. Many variations of the problem have been studied: capacitated VRP, with multiple depots, with time windows etc. To this day, exact algorithms can only solve a relatively small number of cases with highly variable computational times, and heuristics therefore remains the only reliable approach for the solution in practical instances.
This paper analyses the differences between the theoretical and the practical approach to the solution of VRPs, and also describes an algorithm that has been efficiency-tested in the solution of a real-life VRP
The key role of quality assessment in public transport policy
No full textThis paper reviews assessment methods on transit quality, their application in stating the relationship with the demand for a certain service, and briefly the consequences in terms of transport policy of
the process of transit quality assessment.
This is discussed outside the context of the more familiar “predict and provide”method to an integrated transport policy, as the interdependency of quality and demand for a public transport service is generally hard to estimate, due either to the presence of a number of different significant criteria for quality assessment or to a quite strong dependency from subjective impressions of the customers.
Shortcomings are also connected with the presence of a number of intangibles.
All these causes make hard to distinguish sufficiently between those factors that are important for customers’ quality evaluation, and
those that are not.
The paper suggests a step-by step approach based on the joint use of customer satisfaction surveys and transit performance measurement techniques for determining what specific criteria really matter to customers, and highlights the importance of understanding more about passengers actual journey quality for an informed judgement on the impact of future schemes as a hint for policy makers
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