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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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
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Evangelia Kontaxi – Via Eudossiana 18, Italy, Tel : +39 06 44585144, Fax: +39 06 44585144 , E-mail:[email protected]