Influence of train control system characteristic on railway infrastructure capacity.
Haramina, Hrvoje ; Brabec, Dean ; Stefancic, Igor 等
Abstract: Division of the railway line into fixed blocks of the
pre-determined length often fails to be adapted to those trains that
have shorter braking distances. Thus, the headways of the slower trains,
regarding their longer bloking times, affects negatively the line
capacity and therefore represents one of the essential reasons of
reduced efficiency of rail traffic. By comparing the relative distance
in the sequence of two successive trains which is achieved by different
types of train control systems it is concluded that the possibility of
train sequence at shorter distances, that does not reduce at the same
time their speed, increases the line capacity.
Key words: train control system, railway infrastructure capacity,
automatic train protection
1. INTRODUCTION
The division of the open railway line into several blocks allows
simultaneous sequence of several successive trains on the open railway
line between two railway stations and results in its greater capacity
(Badanjak, et al., 2007). One of the essential problems in this type of
protection is that the open railway line is divided into fixed blocks of
the pre-determined length. The basic rule of rail transport safety,
namely, lies in the fact that the minimal block length has to contain at
least the value of the longest stipulated train braking distance on this
section of the railway line, and since this distance is different for
different trains the longest one is always the valid one (Pachl, 2004).
Such division of the railway line often fails to be adapted to those
trains that have shorter braking distances in which the headways of the
slower trains on the open railway line divided into fixed blocks longer
than those that, regarding their dynamic characteristics, and especially
their braking distances, would be really necessary, affects negatively
the line capacity and therefore represents one of the essential reasons
of reduced efficiency of rail traffic.
2. COMPARISON OF VARIOUS TRAIN CONTROL METHODS REGARDING LINE
CAPACITY
Train control methods that encompass the division of open railway
line into several blocks include:
* train control on open railway line divided into fixed blocks by
discrete influence on the train;
* train control on open railway line divided into fixed blocks by
continuous influence on the train;
* train control on open railway line by the application of the
safety moving block system.
When the open railway line is divided into several fixed blocks
that can be controlled regarding occupancy by railway vehicles the
length of distance spacings depends on the necessary length of the
blocks that maximally meet the requirements for safe and efficient
operation of rail traffic. The rule is that the minimal length of the
block has to contain at least the value of the longest stipulated train
braking distance on this railway line section. In case of such method of
train control on the open railway line, several trains can operate
simultaneously in one direction, which increases the line capacity. In
case of such operation method the Automatic Train Protection system
prevents through its automatic action the train from running along
uncontrolled train route on the open railway line when the person
operating the train, for any reason whatsoever does not perform the
action predicted by the aspect of the block signal. In that case the
train protection can be realised by installing inductive balises which
act in accordance with the aspect of the block signal on the equipment
installed onboard train, which allows, if necessary, train velocity
control or its automatic stopping if the train running method endangers
the traffic safety.
In train control system in which the system of cabin signalisation
is applied by installing additional devices in the form of electronic
balises and electromagnetic loops for the transmission of coded
information the usage of the railway line can be additionally improved
by increasing its capacity and the traffic safety can be increased by
additionally influencing the method of vehicle running in specific
traffic situations. An example of such a train control system is also
the ETCS Level 1 (European Train Control System Level 1) in which the
control information is sent in a discrete way via special track balises
called Eurobalises to the train by means of radio connection. Based on
the received control information the computer onboard train continuously
controls and calculates the speed profile and train braking curve. One
of the essential problems in this method of protection is certainly the
fact that the open railway line is divided into fixed blocks of
pre-defined length. This length does not correspond equally to different
types of trains regarding their relevant characteristics such as
acceleration, braking, maximal technical speeds, masses, lengths, etc.,
and this results in the reduction of the possibility of optimal rail
traffic operation. Moreover, the control information that can affect the
optimisation of train traffic in certain unplanned situations in train
traffic can be transferred to the train only at certain points on the
railway line which additionally represents a barrier in the optimisation
process of the real-time train control. This is precisely the reason for
the tendency to apply the train control system with continuous influence
on the train.
Unlike the discrete influence on the train, namely, in case of
continuous influence on the train the control information can be
transferred to the train at any moment during its running along an open
railway line. In this way the train can respond at any moment to the
changes in traffic. Besides, the application of continuous action on the
train in the process of control allows the increase in speed. Since the
length of blocks is determined regarding the length of the braking
distance of a certain train and its maximal speed, for the successive
train to be able to run at a speed higher than the speed for which the
braking distance of the respective train does not exceed the block
length of the open railway line to which the train is arriving, it is
necessary to provide a longer length of the free space in front of the
successive one so as to avoid its conflict with the preceding train.
This can be solved in several ways. The first is to increase the lengths
of fixed blocks with the reduction of their number, thus in case of the
running of slower trains there is the problem of reduced line capacity.
Another is to organise the sequence of successive trains on three blocks
which again in case of the operation of slower trains can cause reduced
line capacity. It is precisely for these reasons that the need occurs to
solve the mentioned problems by the application of continuous influence
on the train. Some of the better known examples of solutions of control
by the application of continuous influence on the trains in Europe are
the systems LZB, TVM and ETCS Level 2.
The train control by the application of the LZB system (continuous
influence on the train) only those trains are continuously influenced
that are equipped by devices of this system, by transfer of the control
information via inductive loops laid on the tracks. The train control,
namely, by the application of the LZB system is most frequently
performed parallel with train control using the classical system with
the division of railway lines into fixed blocks and by discrete
influence on the train, with high-speed trains using LZB, and all the
others using the classical system of train control. The railway line for
the running of trains controlled by the described system of discrete
influence on the trains that operate along fixed blocks, based on the
aspect of block signals, is only supplemented by the LZB system that
directly acts only on those trains that are equipped for this train
control method. Thus, trains controlled by the LZB system by means of
cabin signalisation receive the control information about the maximally
allowed running speed on a certain section of the protected route which
is displayed onboard train by means of an interface to the engine
driver. This is precisely the reason why the train can reach higher
speed also on the railway lines where its braking distance at that speed
is longer than the length of blocks, unlike the case in which, if it
were controlled by the aspects of the block signals its braking distance
had to be shorter or equal to the block length. Thus, in this case, the
solution has been reached which increases the running speed of certain
trains on the open railway line without affecting the length of the
blocks that remain adapted to the running of slower trains controlled by
the system that understands the traffic regulation by means of block
signals. The control of the tracks condition and the integrity of trains
are performed on the basis of the control of the occupancy of the tracks
of each individual fixed block. The TVM system (Transmission
Voie-Machine--"transmission from railway line to train") also
has a similar operation principle which is applied on the high-speed
railway lines (Ligne a Grande Vitesse--LGV) in France.
Unlike LZB and TVM, in the ETCS Level 2 system the continuous
transmission of control information is performed in the wireless way by
means of GSM-R system (Global System for Mobile Communications for
Railways) which originated as part of the ERTMS project started by the
International Railway Union (UIC) as result of the tendency for
technical harmonisation of railways in the countries of Europe, and
wider.
Unlike the mentioned method of train control whose basic
characteristic is the existence of the so-called fixed blocks that are
pre-dimensioned and set depending on the rail traffic characteristics on
a certain railway line and separated by signals, there is also the train
control method in the so-called moving block. The moving block train
control system does not require the track circuits or track contacts
with axle counters in order to determine the position of the trains and
their integrity but it rather relies on the continuous two-way digital
radio communication between every controlled train and the control
centre as well as on the equipment onboard train which checks its
integrity. In case of control systems that include the application of
the train control method in the moving block, the railway lines are
usually divided into the control areas where each is controlled by means
of a computer at the train control centre with the transmission of
control information by means of radio communication system.
Every train transmits data about its identity, position, direction
of movement and speed to the computer that controls the control area in
which a certain train is positioned. Based on the gathered data the
computer performs the calculation of the necessary length of the gap
between the trains that are within its region. The radio communication
connection between each train and the computer is continuous so that the
computer has all the data on the position of all the trains within its
area at any moment. The computer forwards to every train the data on the
position of the train it follows and stipulates the curve of braking
necessary to stop the train before it catches up with the train ahead.
The basic advantage of the moving block system over the fixed block
systems lies in the fact that the position and length of the moving
blocks is adapted to the required running method to meet the planned
objectives of traffic control determined on the basis of the position,
dynamic characteristics and actual train speeds on a certain railway
line section.
3. CONCLUSION
The train control systems that are based on the so-called fixed
blocks are based on the rule that only one train is allowed on one
block. This running method has several marked drawbacks that cause the
lack of flexibility of railway traffic. In this case, namely, the length
of the block is set for all the types of railway vehicles regardless of
their different running speeds and braking characteristics. Thus large
safety distances of the fixed block as required by fast trains with
longer braking distances are unnecessarily imposed also for the slower
trains since the minimal length of the fixed block, among other things,
is determined by the needs of the longest minimally necessary braking
distance of trains that can operate on a certain railway line. Unlike
the train control by methods based on the fixed block, the method based
on the moving block does not require track circuits or track contacts
with axle counters in order to determine the position of trains and
their integrity but rather relies on continuous two-way digital radio
communication between every controlled train and the control centre and
the equipment onboard train which checks the train integrity. The basic
advantage of the train control methods based on the moving blocks
compared to the fixed blocks lies in the fact that the position and the
length of the moving blocks adapts to the position, dynamic
characteristics, and actual speed of the train in the area. This fact
can bring a whole number of advantages regarding the realisation of the
planned timetable, especially on the sections of the rail network with
extremely busy traffic.
4. REFERENCES
Badanjak, D.; Bogovic, B.; Jenic, V. (2007). Organizacija
zeljeznickog prometa, Organizing of Railway Transport, FPZ, ISBN 953-243-012-1, Zagreb
Hansen, I. A.; Pachl, J. (2008). Railway Timetable & Traffic,
Eurailpress, ISBN 978-3-7771-0371-6, Hamburg
Pachl, J. (2004). Railway Operation and Control, VTD Rail
Publishing, ISBN 0-9719915-1-0, Mountlake Terrace
Giannettoni, M.; Savio, S. (2002). Traffic management in moving
block railway systems: the results of the EU project COMBINE. Computers
in Railways VIII, Ed. J. Allen, R.J. Hill, C.A. Brebbia, G. Sciutto and
S. Sone, pp. 953-962. WIT Press, ISBN: 978-1-85312-913-1, Southampton
*** (2011) http://www.fpz.hr--Automatizacija u zeljeznickom
prometu, Railway Automation, Accessed on: 2011-08-11
