DECENTRALIZED SYSTEM FOR MONITORING AND
CONTROL OF RAIL TRAFFIC IN EMERGENCIES
A New Distributed Support Tool for Rail Traffic Management
Itziar Salaberría, Unai Gutierrez
Intelligent Transport Department, Deusto Technology Foundation, Bilbao, Spain
Roberto Carballedo, Asier Perallos
Department of Software Engineering, University of Deusto, Av. Universidades, 24, Bilbao, Spain
Keywords: Railway Traffic Management, Distributed System, Wireless Communications, GPS Positioning.
Abstract: Traditionally Rail Traffic Management is performed automatically using centralized systems based on wired
sensors and electronic elements fixed on the tracks. These systems, called Centralized Traffic Control
systems (CTC) are robust and high availability, but when these systems fail, traffic management must be
done manually. This paper is the result of 4 years of work with railway companies in the development of a
distributed support tool for rail traffic control and management. The new system developed combines train-
side systems and terrestrial applications that exchange information via a hybrid mobile and radio wireless
communications architecture.
1 INTRODUCTION
Today, rail traffic management is performed
automatically using Centralized Traffic Control
systems (CTC) (Ambegoda, A., et. al. 2008). These
systems are based on sensors and different elements
fixed on the tracks. These systems allow real-time
traffic management: (a) location of trains, (b) states
of the signals, (c) status of level crossings and (c)
orientation of the needles. Most of the infrastructure
management entities have a CTC that handles
centralized all these issues. The applications and
systems that handle these tasks are very robust and
have a performance index near 100%. Problems
occur when these systems fail. In those situations,
traffic management has to be performed manually
and through voice communications between traffic
operators and railway drivers (Sciutto, G., et. al.
2007).
The work presented in this article is the result of
the work made during the last four years alongside a
regional railway company of Spain. It defines a
support tool to assist traffic operators in emergency
situations in which CTC systems fail. The main
objective of the new system is to reduce human error
caused by the situations in which priority systems do
not work properly.
The paper is organized into the following
sections: the second section includes a brief
description of the main functionality of the new
system developed. The third section details the
technical aspects of the work done. The fourth
section presents the results the tests made. To close,
the fifth section of the paper establishes the main
conclusions of this work and the following steps to
deploy the new system in a real scenario.
2 FUNCTIONALITY
CTC traditional systems are centralized and rely on
wired communications. When CTC system or
communications fail, no one knows the location of
trains, thus increasing the chances of an accident. In
these situations, the railway companies put into
operation its security procedures that transfer the
responsibility of traffic management to traffic
operators, who are people that monitor traffic in the
terrestrial control centers. These people should
manage the traffic manually communicating through
152
Salaberria I., Gutierrez U., Carballedo R. and Perallos A. (2010).
DECENTRALIZED SYSTEM FOR MONITORING AND CONTROL OF RAIL TRAFFIC IN EMERGENCIES - A New Distributed Support Tool for Rail
Traffic Management.
In Proceedings of the 5th International Conference on Software and Data Technologies, pages 152-157
DOI: 10.5220/0003010301520157
Copyright
c
 SciTePress

analog radio systems to the drivers of the trains. As
people get nervous in emergency situations and that
leads to mistakes, the new system aims to reduce
these errors by creating a new tool to help traffic
operators in emergency situations. This new tool
must be based on different technologies to those
used by traditional CTC systems so that failure in
the former does not cause failure in the latter.
Taking into account the aspects mentioned above
we have developed the Backup Traffic Management
Tool. This system will assist traffic operators when
the primary system fails. The main functions of this
new system are:
 Traffic situation representation for the track
stretches where the main system do not provide
information. The new application represents the
affected line stretches situation (train locations,
track section occupation states, etc.) from
information received from train-side systems
through real-time wireless ‘train-to-earth’
communications (see Figure 1).
Figure 1: Traffic situation representation.
 Traffic management environment. The aim is to
assist traffic operators in tasks related to traffic
control when the main system fails partial or
totally.
 Statistical analysis about aspects related to the
system performance and reliability.
 Control message sending from control centre to
trains. This functionality allows traffic operators
to send messages to the train drivers in order to
manage and control the traffic.
The Backup Traffic Management Tool provides a
traffic assistance application that works
independently of the main CTC System. Thus, the
new system is based on an application that informs
about the position of the trains on track and permits
to make tasks related to traffic management and
control in an easier way. Furthermore, this system
permits a new way of communication between the
traffic operators and the trains drivers: exchanging
control messages.
It is important to point out that even if the main
system is working without failure, our backup
system stores train position information received
from the boarded system, and analyzes the
coherence between the information provided by this
new system and the information provided by the
primary system. This analysis is important to
guarantee the reliability of the Backup Traffic
Management Tool. Furthermore, all the stored
information could be used for other external
applications.
The Backup Traffic Management Tool is based
on the following modules: (1) train positioning
system, (2) statistical analysis, and (3) control
message exchanged.
2.1 Train Positioning Module
The Backup Traffic Management Tool is always
receiving and storing positioning information
generated by the train-side systems. Furthermore,
the Backup Traffic Management Tool can receive
positioning information generated by the traffic
management main system due to the existence of an
External Positioning Information System that
publishes the information generated by the main
system via JMS based Messaging System. This
storage tasks are performed even when the primary
CTC system is active because the information
collected will be used for statistical analysis module.
Therefore, this module stores the information
that receives from the main and the backup systems.
This stored information is basic on the generation of
statistics related to the Backup Traffic Management
Tool reliability. These statistics will be used for the
improvement of the system. Furthermore, this
information may be exploited and used by future
applications and systems.
2.2 Statistical Analysis Module
Using the information stored by the positioning
system on a data base, the Backup Traffic
Management Tool can make statistical analysis
related to the system’s reliability level, GPS and
GPRS coverage, and other system functionality
aspects.
Then, one of the main objectives of this module
is to compare the received information, determining
if the positioning provided by the train-side systems
agrees with the information generated by the main
CTC system.
2.3 Control Message Exchanged
Module
This module allows the procedural alarms
transmission to the train-side systems.
DECENTRALIZED SYSTEM FOR MONITORING AND CONTROL OF RAIL TRAFFIC IN EMERGENCIES - A New
Distributed Support Tool for Rail Traffic Management
153


Figure 2: Backup Traffic Management Tool.
The procedural alarms indicate anomalous
situations: main system failure, signal exceeds
authorization to a certain point as a consequence of a
failure of any electro-mechanical track component,
etc.
Moreover, taking into account the different
circumstances that can occur, and notifications given
to engine drivers, there are two types of messages:
 Messages generated by the traffic operator: the
traffic operator in the terrestrial control centre
can select and send messages manually to a train
driver. These messages must be confirmed
immediately by the driver when they read them
on the HMI.
 Temporal speed limitations: these messages are
predefined by a circulation inspector and they
have greater validity than the others. Once the
message is created, it is sent to all the trains
immediately.
3 TECHNICAL DESCRIPTION
In this section, we describe the most important
technical aspects about the proposed system. The
main aspects are related to (1) trains positioning and
(3) wireless ‘train-to-earth’ communications. Both
issues are described below.
3.1 Train Positioning Information
Generation and Management
The Backup Traffic Management Tool permits a new
way of train positioning which works independently
of the main system operation. This system receives
and stores positioning information generated by the
hardware (accelerometers, gyroscope, odometer,
etc.) and GPS modules boarded on the trains.
Furthermore, the Backup Traffic Management Tool
communicates with an external positioning
information system which permits the reception of
train positioning information generated by the main
CTC system.
Figure 3: Train Positioning Reception in the Backup
Traffic Management Tool.
3.1.1 Train Positioning Generation Based on
GPS
In order to enable a new way of train positioning
generation and management, the presented system
aims to board a new hardware/software module on
each train. This system is based on GPS data and it
is able to generate train positioning information
applying a logical approximation algorithm for
matching railway lines and GPS coordinates (Wei,
S.G., et. al. 2009). Then this positioning information
is sent to the control center in real-time, so that the
backup application can represent the train location in
a synoptic.
In order to generate the most accurate
positioning information, this system parts from a
railway lines different tabulation ways. In this case,
the tabulation is related to lines lengths (in
kilometers) and the traffic signals positions. Based
on this information, and the data extracted from the
hardware and software modules boarded on trains
(including GPS), this system translates this
information to kilometric points. A kilometric point
is a metric used by the railway company to tabulate
the lines where its trains circulate. So, it can be said
that this system is capable of making a translation of
GPS positions to kilometric points tabulated by the
railway company.
The transmission of train positions to the
terrestrial control centre depends on the
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communication availability. Therefore, all the
positions generated by the boarded system are stored
locally on the trains in log files. These log files will
work as a registry that permits to know what
positions were not sent due to communication and
coverage problems. Furthermore, the information
contained by these logs can be integrated offline
with the Backup Traffic Management Tool in order
to guarantee system reliability.
Besides the position of trains, it is also necessary
to know the exact track each train takes. This is
especially complex because the GPS positioning
accuracy is around three meters, and the tracks are
separated by less than 2 meters. To achieve the exact
track that occupies a train inertial sensors are used.
These sensors allow the detection of tack changes.
Finally it is noteworthy that for sections of track
without GPS coverage distance and speed data are
used to determine the exact position of the trains.
As it can be guessed, the positioning module has
been the most complex to develop because we have
had to perform multiple tests outside the laboratory
to refine the different types of positioning and to
combine them appropriately.
It is important to remark that this positioning
system has been developed based on standards;
therefore, it is possible a migration to another
navigation satellite system like Galileo, or the
combination of GPS and Galileo in the future,
creating an even more accurate global navigation
satellite system.
3.1.2 Communication with the External
Positioning Information System
The external positioning information system’s aim is
to provide train positioning information generated
by de main CTC system to other external systems.
This system is based on JMS (Java Massaging
System) in a publish/subscribe schema. So, the
messages published by the CTC system can be
received by the subscribed applications.
In order to generate reliable statistics about the
proposed system with respect to the original system,
the Backup Traffic Management Tool subscribes to
the External Positioning Information System to
receive positioning information generated by the
CTC.
3.2 ‘train-to-earth’ Communications
Module
The system presented on this paper permits a real-
time train traffic management, so it is necessary to
enable a wireless communication channel between
the Backup Traffic Management Tool installed on
the control centre and the trains. For this reason, the
system that we propose in this paper uses a ‘train-to-
earth’ wireless communications architecture based
on mobile and radio technologies (Salaberria, I.,
Carballedo, R., Gutierrez, U., Perallos, A., 2009).
Figure 4 shows the basic protocols and
communication technologies applied in the
communications architecture.
3.2.1 Protocols
The communication between the terrestrial and the
on-board system is based on REST
(Representational State Transfer) technology. This
communication technology uses the HTTP
(HyperText Transfer Protocol) protocol and XML
formatted messages. This solution is similar to
traditional XML Web Services but with the benefit
of a low overload and computational resources
consumption (Pautasso, C., Zimmermann, O.,
Leymann, F. 2008). Although the information
interchanged between the Terrestrial and the On-
Board Communication Managers is encrypted, using
the HTTP protocol allows the easy migration to
HTTPS (HyperText Transfer Protocol Secure) that
offers encryption and secure identification.
It is important to point out that REST is not a
standard; it is an architecture style that is based on
standards (HTTP, URL, XML/HTML/GIF/JPEG/..
resource representations, MIME types, etc.).
In addition, it can be said that the selected
technologies are well known and broadly used in
different application areas or contexts, but they are
novel in the railway train-to-earth communication
field.
Figure 4: ‘train-to-earth’ Communications Architecture.
3.2.2 Communication Technologies
In order to establish ‘train-to-earth’
communications, the system presented in this paper
combines mobile (GSM/GPRS) and radio
technologies (WiFi). In this case, according to the
transmission characteristics (information volume,
real-time communications needs, coverage and
DECENTRALIZED SYSTEM FOR MONITORING AND CONTROL OF RAIL TRAFFIC IN EMERGENCIES - A New
Distributed Support Tool for Rail Traffic Management
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communications costs), the system combines these
technologies selecting the best way of
communication in each moment, taking into account
train locations, and its connectivity state (Shafiullah,
G., Gyasi-Agyei A. and Wolfs, P. J., 2007).
To make this communications possible, the trains
have been equipped with the necessary connectivity
hardware/software system. Furthermore, taking into
account mobile communications coverage aspects,
to enhance trains GPRS connectivity, the
communication system boarded on trains allow
GPRS communications within two different
telephony providers, working one of them as main
provider, and the second one as the secondary when
the first one is not operative.
So, in this system movable technologies such as
GPRS/UMTS/HSPA are used for the Real Time
Communications. These technologies do not offer
either a great bandwidth or 100% coverage, and they
have a cost associated to the information
transmission. Despite this, these technologies are a
good choice for the delivery of high-priority and
small sized information. The selection of the specific
technology (GPRS/UMST/HSPA) depends on
whether the service is provided or not, (by a
telecommunications service provider), and the
coverage in a specific area.
On the other hand, this system use WiFi radio
technology to realize ‘train-to-earth’
communications on WiFi connectivity equipped
railway infrastructure points (a private net of access
points is needed). What is more, this technology
allows the transmission of large volumes of
information and does not have any costs associate to
the transmission (for example log information stored
on trains, or train services information that is
uploaded on train periodically).
For a correct and optimized used of the
communication architecture, we have defined two
types of transmission. These two types take into
account characteristics of both information and
communication technologies, such us: the volume
and the priority of the information, the existence of
coverage, and the cost of the communication.
Considering these aspects, we have defined: Slight
and Heavy Communications.
 Slight Communications: This type of
communication is for the transmission of small
volumes of information (few kB.) and with high
priority. In general, information that has low
latency (milliseconds or a pair of seconds) and
needs to be transmitted exactly when it is
generated or acquired (for instance, the GNSS
location of a train, or a driving order to the train
diver).
 Heavy Communications: This type of
communication is tied to the transmission of
large volumes of information (in the order of
MB) and with low priority. The importance of
this information is not affected by the passage of
time, so it doesn’t need to be transmitted at the
exact time it is generated. The management of
this type of transmission is the core of this paper.
It is important to point out that although each
separate technology can’t achieve 100% coverage of
the train route, the combination of both comes very
close to complete coverage. As the application layer
protocols are standard, other radio technologies such
as TETRA or WiMAX can easily substitute the ones
selected now. These technologies can achieve a
100% coverage and neither one has a transmission
cost. However, there are certain limitations such as
the cost of deploying a private TETRA network, and
the cost and the stage of maturity of the WiMAX
technology (Aguado, M., et. al. 2008).
4 EXPERIMENTAL RESULTS
The work that has been presented on this paper is the
result of almost three years of joined efforts with a
railway transportation company.
Currently this system is on real deployment
phase. Thus, the system has been deployed in a
passenger train and in two freight transportation
locomotives, allowing the sending of GPS based
positioning information from trains to terrestrial
control center.
We have performed test on laboratory and also in
real scenarios. Laboratory tests have been
satisfactory. Test on real settings have also been
successful except for mountainous landscapes with
numerous tunnels where wireless mobile
communications were affected by the insufficient
coverage related to these kind of technology.
However, this difficulty can be easily overcome
using a communication technology with a greater
coverage. Furthermore, in order to ensure security
on traffic management, coverage in all stations is
guaranteed. So that, the Backup Traffic Management
Tool is able to recognize when a train enters or
leaves a station, helping to prevent conflicting
movements (interlocking).
It is important to point out that during the system
real tests, there has been improvements on the GPS
based position generation and management. This
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work has been focused on what it is the best way to
relation the position provided for CTC (track
sections) and the position generated by GPS based
boarded system (kilometric points). So, the CTC
provide positions as a track sections where the train
is. This track section is a range of kilometer points.
Therefore, when the backup system receives train
boarded system’s position, it calculates what track
section corresponds to the kilometer point provided
by this position. However, while CTC generates
track section based positions when the train enters or
leaves this track sections, the boarded system
provides the kilometric point calculated by the GPS
module on the main coach where the engine driver
is. Thus, it is possible that the backup system
interprets that there is no correspondence between
both positions when really there is. So, these aspects
have been considered to make improvements to
achieve a better fit between the positions provided
by both systems.
5 FUTURE WORK
In the future our efforts will be focused on (a) the
improvement of GPS based positioning system
enabling a more accurate position calculation, (b)
improvement of communication capabilities and (c)
system deployment and integration with new train
series and other railway lines topology.
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