SNCF - Direction de la Recherche et de la Technologie

Transcription

WCRR Köln November 2001
SISYFE: a toolbox to simulate the railway network functioning for many
purposes. Some cases of application.
WCRR KÖLN, November 2001
Michèle FONTAINE
Daniel GAUYACQ
SNCF - Direction de la Recherche et de la Technologie
45, rue de LONDRES
F-75 379 PARIS CEDEX 08, FRANCE
Telephone: 33 1 53 42 92 40 - 33 1 53 42 92 74
Facsimile: 33 1 53 42 00 47
E-mail: [email protected] - [email protected]
Summary
The railway system, defined by: trains running, signalling and driver behaviour, is very
complex. Its dynamic behaviour cannot really be studied analytical. This complexity is a
result of the mutual interdependence between the signalling system and the running of the
trains. To overcome this difficulty in studying the traffic, simulation is a very good
compromise. The real system can be mimicked to gain flexibility and convenience in
investigating the system’s functioning when changing different hypotheses of behaviour of its
components.
The SNCF research department has developed a software toolbox named SISYFE to
allow to model the railway network with different: signalling systems, types of train products,
categories of rolling-stock and driver behaviour. It is used to implement many applications
and dedicated tools to solve a large range of problems: educational systems for signalmen,
decision support systems to evaluate the different investments needed to upgrade line capacity
or to calculate the robustness of a timetable confronted to small traffic incidents (delayed of
trains, temporary speed reduction). A general presentation of this toolbox is given in this
document completed by a short presentation of case studies for above mentioned problems.
Keywords: discrete-events, simulation, railway network, investment, teaching, robustness,
timetable.
1. Introduction
With a simulator we can easily make the railway network’s process virtual and play
with this artefact like a toy. With this software; traffic problems, delays, locomotive or signal
failures, etc. can be generated. Then, over a longer duration, the results concerning
punctuality of trains can be observed and the delays at each station of its stopping pattern can
be measured. With this, experts can test new strategic decisions to limit the disturbances.
They can also study improvements induced by modification of the railway network such as
signal positioning, modifying turnout properties, adding routes and tracks for over-intensively
used section of lines, etc.
Experts on traffic management can test new strategies to be applied for the scheduling
of train' traffic in real time. For example, they can evaluate the advantages of a new concept
for control and command systems, like ERTMS. Studies can be made for different versions of
ETCS to compare them to classical and proved systems. Before using a new line such as the
TGV Méditerranée in operation, the signalmen in charge of the future circulation can be
trained to handle potential traffic breakdowns. This is a short list of the problems that face a
SNCF DRT - SISYFE - 370.doc
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simulator. It is able to bring substantial help to solve or at least to reduce the cost of a poor
quality in day-to-day production. To meet these various needs, the research and technology
department of the SNCF, has written the SISYFE software. However, the term “library of
software components” would be more appropriate to better characterise this set of dataprocessing programs. It is already been used to implement various specialised applications.
After a statement of the context and the steps of recourse to simulation, a short presentation of
the software SISYFE will be made. Then, various cases will be described.
2. Why simulate ?
Basically the scientific knowledge is being fed and expanding by collecting
observations and defining relationships between the collected facts. When a lot of information
is gathered, empirical or statistical laws can be projected that allow (when considered
probabilistically true) to deduce and to forecast the behaviour of the subject in study before
real observation can be done. The simulation technique can provide, at low cost, a big amount
of information. To be used for that purposes with no fear the simulator behaviour must fulfil
one condition: to be a good reflection of the real system.
The complexity of the problems to be solved in reality, the means and the time that
would be necessary to implement and to examine the different possibilities in real life, are
often incompatible with the requirements of effectiveness and speed. "To simulate, it is to
obtain the information produced by imaginary experiments."
3. Modelling the system to be studied
To simulate, it is necessary to first create a logical and mathematical model of the
system of which the behaviour has to be reproduced. This modelling process transposes in a
particular form the complexity of an already existing or imagined system. Inevitably, this
transcription introduces a bias, which has to be considered and puts in perspective with the
expected results.
The definition of the studied system, used in this article, is based on three axioms:
1. it constitutes a coherent set for the object of the study.
2. it is interacting with an environment. The exchanges between the system and its
environment partly influence the evolution of the system.
3. the internal dynamic of the system is, essentially, self-regulated.
The railway system such as it is described in SISYFE, comprises two main subsystems
that interact. These two components are identified as the mobile and its driver and the fixed
installations of the rail network. The human action of men outside this system (signalmen or
traffic managers) can be assimilated into its environment.
4. Application domains
Three big domains were identified to profit from the simulation of the railway system:
1. studies concerning the global railway system or limited to some of its components.
2. training for tasks connected to the operational management of the rail traffic.
3. testing and functional validation of systems belonging to the domain defined as the
environment of the railway system that interacts with it.
In the first case, simulation finds its legitimacy from the practical impossibility to deduce, for
a significant duration (a few hours), the behaviour of the system by means of an analytical
approach because an analytical approach is impossible.
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For the two other points, the simulation constitutes an extraordinary technique to
acquire knowledge, because it makes it possible to systematise the research for predefined
hypotheses. For these cases, the most favourable type of research consisted of trial and error.
Simulation, by creating virtual worlds, makes it possible to acquire quickly, and at lower cost,
this type of knowledge. These realistic fictions make it possible to test without risk the
sometimes catastrophic assumptions. They are thus fabulous accelerators to acquire an
invaluable experiment.
5. The SISYFE toolbox
5.1 Functional architecture
The core of simulation makes it possible to reproduce simultaneously the changing state
of signals and the evolution of the mobiles. These two parts are the heart of SISYFE’s
software. During a simulation exercise, the intermediate results are displayed via three types
of diagrams presenting: the space/speed diagram, the space/time diagram and the running of
the trains on the network. Correlatively a great masse of data are produced and stored. When
the simulation exercises exist, these data can be treated using tools for statistical analysis to
make synthesis and to produce quantified reports. Upstream of the module, a graphic editor,
coupled to a data base, allows to capture the data describing the railway network (tracks,
signals and switches positioning) and the dynamic logic of signalling.
5.2 Logic of functioning
Without introducing a bias, the railway system can be modelled to a discrete events
driven system. At every moment t, t (the state of the system) is determined by the former
states and the nature of the actions, at-1 sent by the environment (signalmen for the essential).
It is a quasi deterministic system of which the state future t+1 := f ( t ; at) is obtained using
relations of transition checking consistency conditions. The mains events taking into account
are: the crossing of a signal by the front or the back of a train, the stopping or departure of a
train at or from a station, the positioning of a switch, etc. These events appear with irregular
intervals but between two consecutive events the behaviour of the system is without
alternative and completely constant. This characteristic is exploited to determine the final
state starting from the succession of its intermediate states.
The simulation of the studied system then consists in calculating the series of the states
using an iterative algorithm, the engine of the simulator. At each stage of the cycle, the
elementary functions of transition from the various modelled subsystems are evaluated.
During this step the events postponed that will characterise the following stages, are identified
and positioned on the axis of time. The propagation of the modifications of the system states
at the moment t thus generates the conditions which will characterise the following states.
5.3 The parameter on an simulation exercise
To run an exercise of simulation three categories of data can be capture and merge into
the software to describe assumptions to be tested. First, we need to describe the railway
network, second we will depict trains and finally the failures of some system components.
5.3.1 Description of the railway network components
These components are defined mainly in term of graph of the network The profile of
the tracks (its radius of curvature and its declivity) are linked to that. The positioning of
signals and their potential states depending on the signalling system are described too.
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For this last point, three patterns of technical signalling systems are available. They
correspond to: the signalling used on the traditional network, that of high speed network TGV
and that of project ERTMS. The oldest signalling systems can be complemented by three
alternatives of control speed systems (KVB, KVBP, KVIM). They stop the trains which not
respect the instructions indicated by signal (in fact signal colours).
These reference signalling models are based on generic functions that ensure, by information
transmitted to the driver, that advancement can be made in safety. These functions are
assumed by all existing signalling systems.
For that, a system of signalling carries out controls which make it possible to assume three
principal functions:
1. the spacing of trains running to avoid the collision with train that follows.
2. the insurance of continuity of the route in order to prohibit that a turnout is not
operated when a train is near or already in on that zone.
3. the protection to prevent the collision of two trains circulating on the same way but on
opposite direction.
In practice, according to the nature of the signalling system, this information is produced and
transmitted with different techniques.
The signalling system on classical lines
From information of train locations on the network and the orders of switches positioning,
electrical relays ensure the logical equations that determine the nature of the information
carried out by the signals. For the canonical model, four levels of information can be
presented at the driver of the train which may observe the signal:
1. " green ". Authorises a circulation without restriction, subject to not exceeding a speed
limit.
2. " yellow ". Indicates that the train will have to be able to stop at the following signal.
3. " single red". The train must stop at the signal panel. It can then start again at very low
speed to the following signal.
4. " double red ". For the imperative stop.
The first three states belong to function 1, the fourth means that function 2 or the 3 was
activated.
The signalling system working on high speed lines
The TVM signalling system is used on the lines specialised for the circulation of the TGV. It
differs from conventional signalling system on two essential points:
1. the indication of spacing comprises up to six levels of information against three. An
indication of speed is associated to one of these levels and posted on a screen placed in
the cockpil of the TGV.
2. information is transmitted by modulation of an electric signal which circulates in the
rail to be collected by the mobiles.
The new generation of signalling systems
In project ERTMS (ETCS level 2) the principle of localisation of the trains is identical
to that of system TVM. The information transmitted to the mobile is primarily a distance
specifying " an open and protected space " available to the train to progress. The embarked
system (single coded processor of safety) encloses the characteristics of the track and route to
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be crossed (profile, slope) and those of the traction engine. These data are used to calculate
the curve of control speed and to deduce from it the instructions speed and/or braking which
the driver must be apply.
5.3.2 Description of trains
Two categories of data are specified:
1. those describing the timetable which indicates stopping pattern for each train.
2. those corresponding to the physical characteristics of the mobiles (mass, length and
dynamic performances of acceleration and braking). These data consist of the
parameters of a calculation algorithm of running.
5.3.3 Description of failures
In real life, there are two categories of problems. The problems that concern the fixed
installations and those concerning the mobile (the trains). For the former specific failures can
be defined: signal, switches, break of rail, etc. For the latter delay duration for specific train
on a particular station and similar notation for speed reduction on some routes during some
time interval can be defined. These malfunctions constitute the irregularity of operation which
one wishes to measure the consequences on the traffic flow.
5.3.4 Running an scenario
Using these data, the software simulates the running of trains and produces for each
characteristic event a particular data structure of information which makes it possible to trace
the evolution of the system for the set of assumptions tested. Schematically, for each studied
train, according to the information presented by signalling system, its progress to the next
signal is calculated. An algorithm that integrates: the dynamic performances of the mobile, the
distance to be covered, the slope of tracks, carries out this operation. This calculation is
adjusted by factors that simulate the driver’s behaviour.
5.4 Software techniques and tools
An object-oriented design has been retained to describe the various components of the
railway system. This choice is well adapted to the characteristics of the field, because this
methodology makes the description of the various classes of objects in their unit and their
diversity. Then, each category is divided in subcategories (hierarchical and distinct obtained
by the addition or particularisation from attributes and/or functional properties compared to
the mothers classes which bring their fixed value in heritage.)
The software is specified with UML methodology and has been written in C++. It runs on
UNIX. A Windows NT version is under consideration. The interfaces to pilot the software
and the charts were made using the library of C++ object ILOG VIEWS .
5.5 Case studies
Four classes of problems handled with SISYFE are presented below.
5.5.1 Decision support
This kind of studies aim at determining the optimal investments to modify the fixed
installations of the network. The framework of this type of study, has three parts. Experts may
define a goal; different hypotheses are to be identified and considered and the contribution of
each of these alternatives to reach the goal needs to be evaluated. This kind of study can also
be executed to measure the improvement of the performances due to a new signalling system.
The principal requirement can be either to improve the flow of the line or to curb down the
delays. This step was already used to compare the profits in punctuality of circulation on line
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“RER C” which could result from work of modification of the infrastructure of the station of
“Champs de Mars” compared to those induced by the equipment of this line with a moving
block signalling system. To proceed to this type of studies, it is necessary to describe the
existing and/or projected rail network (network schema, signalling, etc.) as well as the
scenarios corresponding for the traffic expected. These descriptions constitute the initial set of
scenarios. The results of the simulations carried out on this basis will constitute a reference
from which the contributions, resulting from the various modifications considered could be
measured. A final step of comparison of cost/advantage then makes it possible to select
installations which seem most effective for the criteria selected. For each typical choice of
investment, the recourse to simulation authorises to calculate the behaviour of the railway
system for various assumptions in the circulation of the trains and/or the availability of the
installations. This facility allows, in a pragmatic way, to apprehend the stability and the
robustness of the solutions considered. But in all cases a great number of simulation of each
hypothesis for slightly changes in parameter need to be done. Only, the observance of this
requirement guarantees in probability that results are true in general and not only true for the
particular cases tested.
5.5.2 Strategies for traffic management
In this category of study, the aim is to identify, a priori, the traffic management rules,
which are most effective to act when certain types of incidents occur. These rules can be
implemented explicitly as a set of advises to treat problems in operational or implicitly
(included on timetable).
Choice of a stopping pattern that improves timetable robustness: the " EOLE " study
This step was used to imagine the way in which future line EOLE could be managed.
This transversal line will connect the east and the west of the Paris area while crossing Paris
in a tunnel. In this study, two ways of operation of the line were considered. To simplify, A is
defined as the station in eastern suburbs, B in the east of Paris, C in Paris-west and D as the
station at the extreme ending in the west.
Banlieue Est
A
PARIS
B
C
Banlieue Ouest
D
Trains Est - Ouest
Trains Est - Paris
Trains Paris - Ouest
Diagram of line EOLE
On the assumption H1 all the trains envisaged to circulate did the whole line between A and
D. On the assumption H2 the cycle of circulation was as follows:
a train going from A to D and then coming back.
followed by a train than A towards C and then coming back.
then, in time synchronisation with the precedent, a train than B towards D and then
coming back.
The experts wonder through these two assumptions, of choosing the "robust" mode of
exploitation when occur of small incidents of exploitation such as the inopportune train stop, a
traveller emergency stop or a repeated delay at each stop caused by a door failure. A priori,
the assumption H2 makes if possible to limit the propagation of the delays along the line. The
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results of the various exercises of simulation showed that this assumption was not confirmed
for the installations (station path, switches, platform) planed initially for station C. However
with some minor adjustments of these installations, integrated in another set of data, it became
possible to prove that H 2 after carrying out these modifications, would make it possible to
provide a better average quality of service.
Choice of a timetable structurally robust: the " Line C " study
Another study was carried out to define the most robust “line C” timetable to absorb
the disturbances of trains circulating. Several timetables, similar in transport capacities
offered to the customers but differently distributed over time, were compared and classified
for the robustness criterion in relation with failures: either of the railway installation or of the
trains. From a starting timetable corresponding, for given direction, to the circulation of six
trains to the fifteen minutes that is to say a train departure every two minutes thirty; with for
alternative a less regular spacing although compatible with the temporal constraints of spacing
of the trains and which makes it possible to release in end of the cycle an interval of recovery.
This margin has the role to absorb the small delays before they explode. In conclusion of this
study, the first principle was adopted, because the too much closer succession of trains
envisaged in H2 made the respect of the schedules very unstable even for weak disturbances.
In conclusion, the selected timetable is based on a two minutes interval thirty. This solution
constitutes a good compromise between the guarantee of a better regularity of the provided
service and the need for proposing schedules easy to memorise.
5.5.3 Training signalmen
The software components of SISYFE were used to produce the software FISSA which
made it possible to carry out the initial formation, in real working situation, of the signalmen
on the Noisy station (a Paris suburb town). This simulator was connected directly to the
devices of that station which made it possible to order the routes and to visualise the
advancement of the trains.
The training of these employees had two goals:
1. to teach them to master the basic commands allowing, in normal situation, a good traffic
management.
2. to make them able to treat disturbances: delays in the arrival of the trains or problems with
fixed installations. For this its may be necessary to apply particular protocols " in safety "
to bypass the errors induced by the disturbed devices.
To achieve the first goal, the simple and easy scenarios, with one train, were simulated. The
person on training was thus put in situation to act on the route setting for this train. Next
various more complex scenarios, integrating the simulation of problems, in particular broken
signals and turnouts, were carried out to do the training for disturbed situations that requires
the application of the safety protocol.
During the training period, FISSA made it possible to make it seem as if the station was really
functioning for the future timetable. In contrary to the normal start-up of new signal boxes,
the operational switch-over was done without tear. In the future this procedure will be
generalised for all similar situations. Moreover, teaching simulators " off line " will be placed
at the disposal of the signalmen in order to improve, “continuously”, their training on traffic
management.
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5.5.4 Testing and validating decision support systems for traffic management
The research department produces also decision support systems for the traffic
management. These tools are based on mathematical techniques of optimisation or artificial
intelligence techniques such as the expert systems. This is the case for software SAFIR. This
tool aims to “smoothen” the train circulation when conflicts are noticed. To ease train traffic
and minimise the delays on complex railway nodes, orders of reduced speed are calculated
and applied to trains before crossing the node. After, the train can pass trough at full speed
and thus gains more time than it lost by this approaching slowly.
During the debugging and the beta test period, to validate the relevance of advice
given, SAFIR has been connected to SISYFE in a configuration very close to that selected to
train the signalmen. The simulator provides information on the advancement of the trains and
the availability of the installations. Using these data SAFIR chooses the routes which allow,
for the criteria selected, to optimise the circulation of the trains. Scenarios of functional
validation were described to check the proposals of SAFIR in disturbed situations, for
example, simulating breakdowns affecting the fixed installations or the mobiles. The choices
made by SAFIR are then transmitted to SISYFE in the form of orders both of: routes and
speeds for trains running. The analysis of the behaviour of the system made it possible to be
sure of the consistency of the solutions suggested either by global measurements, for example,
summing the delays; or by confronting the choices made by SAFIR with those made by the
experts of the field.
6. Conclusion
Until now, the software SISYFE is an exemplary success use case of the techniques of
simulation. The strategy consisting in developing a library of reusable components preferably
with the production of software strictly dedicated to a particular application, proved very
effective. It enabled us to realise, starting from the same "software components", several
applications having each one particular advantages. The use of simulation techniques, to
support decision-making, will experience new developments. Two directions are subject of
the research projects.
The first focus on the use of simulation tool to assist an operational traffic manager in
real time decision-making. This tool will project the observed state of train running for a fixed
temporal horizon. The various examined future states of the system will be given by the
sequence of actions according to the strategies of management available. Each one of these
potential states will be developed according to various criteria of evaluation. The operator can
thus control his decision-making by a good information on the consequences. This
corresponds to a functional specialisation of the study field covered by SISYFE with an
additional requirement on the level of the calculation performances.
The second axis aims to develop simulation based tools for defining specification of
efficient production systems for the railway domain notably for the freight. In this case, the
organisation of work (task to do by workers and number of them) and the location of yards
will be modelled.
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SNCF - Direction de la Recherche et de la Technologie

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