RAILWAY MODELS FOR CAPACITY CALCULATION
Transcript
RAILWAY MODELS FOR CAPACITY CALCULATION
RAILWAY MODELS FOR CAPACITY CALCULATION Evangelia Kontaxi*, Stefano Ricci, University of Rome «La Sapienza», DICEA Department, Italy ABSTRACT The present article analyses techniques, methods and models focused on the determination of railway capacity and classified by reference factors that have a direct correlation with the results obtained. Synthetic and analytical methods, optimization methods and simulation methods are compared. Emphasis is given to the interaction of numerous factors related to the complex structure of the railway system and the conceptual and terminological variety that characterize them. Finally a new interactive and free of use system will be presented in order to offer the possibility to all railway actors to have the possibility to test the different methods and to evaluate the given numerical results. Keywords: Capacity, Methods, Techniques’, Models INTRODUCTION Looking forward to the best use of available resources is of major importance the calculation of railway capacity. The continuing growth in demand for rail transport services (passengers and freight) leads to an increasing use of rail infrastructure. The approach of the problem, very complicated because of various factors, has been analyzed in several aspects. The methodological framework under examination consists of all methods which have been developed since 1950 and have been continually updated to our times. Several factors have given inspiration to this analysis, with the sole aim of offering a spectrum of choices and integration of different methods. The rail capacity, however, is a difficult concept to define and compute. The difficulty is due to the interaction of numerous factors related to the complex structure of the railway system and the conceptual and terminological variety there. The themes proposed are continuously evolving as the subject is wide and meets many developments and applications around the world. Since the presence of European methods and / or simulation tools is very strong, not only in educational environments but also in managing companies of railway traffic and infrastructure, the need for a tool that can provide all answers is evident. One aspect, of the available developed methodologies and techniques for the determination of rail capacity, is that almost all of them are perfectly integrated with the needs of time and operational context in which they have been developed but are not always adaptable to generic requirements. There is, therefore, the need to promote the communication and cooperation between private and academic sectors to further incentivize the development of a new integrated use for the calculation of railway capacity and to facilitate the exchange of knowledge and experience between them. Railway Capacity The “Railway capacity” theme is a combination of the capacity consumption and its differentiated utilization, which can be divided into 4 core elements: the number of trains, the average speed, the heterogeneity of the operation, and the stability. Capacity, whose definition is a classical problem, has long been a significant issue in the railway industry. The goal of capacity analysis is to determine the maximum number of trains that would be able to operate on a given railway infrastructure, during a specific time interval, given the operational conditions. This definition emphasizes the dynamic nature of capacity and identifies the fundamental factors that affect it. It recognizes that capacity is not static. Classification of techniques and methods The different techniques and methodologies for calculating the capacity can be divided into three main categories according to the used methodology, the compiled data and the level of detail. They are: • Synthetic: they use deterministic expressions, i.e. the variables contained in these cannot change its state and assume fixed values during the reference time; from the mathematical point of view they are equations were the unknown quantities are mutually independent, they are also called static; • Analytical: they use probabilistic expressions; from the mathematical point of view they are equations were the unknown quantities are mutually dependent, they are also called dynamic; • Analogical: can be further divided into asynchronous methods (this covers methods which provide the optimization of one or more variables) and synchronous methods (traffic simulation), for instance the optimization methods are based on procedures looking for delays minimization in the mixed speed traffic, as well as the simulation methods represent the evolution of advanced research and are often used to validate the results of other methods. Analytical methods model the railway infrastructure by means of mathematical expressions in a simple way that provides results of a first approximation, the optimization methods are based on research and best saturated schedules while simulation methods provide models capable of representing the reality in order to validate the timetable data. Referring to these, multiple products, which normally generate timetables by Evangelia Kontaxi – Via Eudossiana 18, Italy, Tel : +39 06 44585144, Fax: +39 06 44585144 , E-mail:[email protected] 2nd International Conference on Models and Technologies for Intelligent Transportation Systems 22-24 June, 2011, Leuven, Belgium simulation using the laws of motion of trains are developed and then marketed. The simulation environments are tools available on the market, which dialogue with the user interface and simulate rail traffic. Usually they generate timetable graphs dynamically defined through equations in which the time is a fixed variable in defined intervals. A detailed analysis was carried out on a total of 49 methods and 37 simulation environments so far. An extensive differentiation of methods which deal with node’s capacity and line capacity has also been performed. For all techniques and methodologies which have been examined, an electronic database has been created which is clearly not exhaustive, but allows "comparing" all the aspects that are covered by the term "railway capacity”. The railway capacity assessment tool The formulation and development of an integrated instrument characterized by different degrees of detail, therefore, useful for academic, technical-scientific and operational scopes has been created. One of the primary goals of the present research is to propose a railway capacity assessment tool in order to offer a complete methodological framework analysis of railway capacity calculation. This instrument will be available on the web and free of use, for everyone who takes part of academicals institutions and/or technical-scientific, operational backgrounds. It’ purposes is to offer: • free use of the results of the present research • comparative analysis of available methodologies and techniques relative to the capacity calculation of a railway system (line and/or nodes) • technical manual of all theories which have formed during the past years the different methodologies • intelligent calculator friendly to use directly on the web. The best environment which can host such an instrument is the internet portal therefore the authors have decided to create a website where all the above functions can be solved. Today, the internet site is still under construction but its main structure is completed. The main structure of the instrument is based on the following tasks: • Definition of the available input data by the user • Elaboration of the input data and performance of an intelligent choice by the instrument which will redirect the user to the definition of the methodologies which can perform the capacity calculation based on the input data. • Brief methodological description of available techniques along with comments regarding their advantages and disadvantages. In the future, a SWOT analysis of each one of them will also be available. • Consequently to the user selection of the most appropriate method, a redirection to a dedicated interface will consent the numerical calculation of the railway capacity. The integrated instrument will as well provide a list of commercial simulation tools available on the base of the input data along with a SWOT analysis for each methodology. 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