6 ◾ Advances in Communications-Based Train Control Systems
– ATS.is system is commonly integrated within most of the CBTC solu-
tions. Its main task is to act as the interface between the operator and the
system, managing the trac according to the specic regulation criteria.
Other tasks may include the event and alarm management as well as act
as the interface with external systems.
– Interlocking. When needed as an independent subsystem (for instance, as
a fallback system), it will be in charge of the vital control of the trackside
objects such as switches or signals, as well as other related functionality.
In the case of simpler networks or lines, the functionality of the interlock-
ing may be integrated into the wayside ATP system.
– Wayside ATP. is subsystem undertakes the management of all the com-
munications with the trains in its area. Additionally, it calculates the limits of
movement authority (LMAs) that every train must respect while operating
in the mentioned area. is task is therefore critical for the operation safety.
– Wayside ATO. It is in charge of controlling the destination and regula-
tion targets of every train. Its functionality provides all the trains in the
system with their destination as well as with other data such as the dwell
time in the stations. Additionally, it may also perform auxiliary and non-
safety-related tasks including, for instance, alarm/event communication
and management, or handling skip/hold station commands.
2. CBTC onboard equipment. It includes ATP and ATO subsystems in the vehicles.
– Onboard ATP. is subsystem is in charge of the continuous control of
the train speed according to the safety prole and applying the brake if it
is necessary. It is also in charge of the communication with the wayside
ATP subsystem in order to exchange the information needed for a safe
ATS
Wayside ATP Interlocking
Wayside ATO
Train–ground radio communication system
Onboard ATP
Onboard ATO
Onboard ATP
Onboard ATO
Figure1.4 Typical architecture of a modern CBTC system.
Introduction to Communications-Based Train Control ◾ 7
operation (sending speed and braking distance and receiving the LMA for
a safe operation).
– Onboard ATO. It is responsible for the automatic control of the traction
and braking eort in order to keep the train under the threshold estab-
lished by the ATP subsystem. Its main task is either to facilitate the driver
or attendant functions or even to operate the train in a fully automatic
mode while maintaining the trac regulation targets and passenger com-
fort. It also allows the selection of dierent automatic driving strategies to
adapt the run time or even reduce the power consumption.
3. Train–ground radio communication subsystem. It is one of the key technolo-
gies in CBTC systems. Wireless networks, such as Global System for Mobile
Communications—Railway and wireless local area networks (WLANs), are
commonly used to provide bidirectional train–ground communications.
For urban mass transit systems, IEEE 802.11a/b/g-based WLANs are a bet-
ter choice due to the available commercial o-the-shelf equipment and the
philosophy of open standards and interoperability.
1.4 Challenges of CBTC Systems
Although there are many advantages of CBTC systems, several signicant research
challenges remain to be addressed to make CBTC systems safer, more reliable, and
ecient.
e primary challenge of a CBTC system is that if the radio communications
link between any of the trains is disrupted, then all or part of the system might have
to enter a fail-safe state until the problem is remedied. Communications failures
can result from equipment malfunction, electromagnetic interference, weak signal
strength, frequent hando, or saturation of the communications medium. Building
a train control system over wireless networks is a challenging task. Due to unreli-
able wireless communications and train mobility, the train control performance
can be signicantly aected by wireless networks. is is the reason why, histori-
cally, CBTC systems rst implemented radio communication systems in 2003,
when the required technology was mature enough for critical applications.
Depending on the severity of the communication loss, this state can range from
vehicles temporarily reducing speed, coming to a halt, or operating in a degraded
mode until communications are reestablished. If communication outage is perma-
nent, some sort of contingency operation must be implemented, which may consist
of manual operation using absolute block or, in the worst case, the substitution of
an alternative form of transportation. As a result, high availability of CBTC sys-
tems is crucial for proper operation, especially if we consider that such systems are
used to increase transport capacity and reduce headway. System redundancy and
recovery mechanisms must then be thoroughly checked to achieve a high robust-
ness in operation. With the increased availability of the CBTC system, the need
8 ◾ Advances in Communications-Based Train Control Systems
for an extensive training and periodical refresh of system operators on the recovery
procedures must also be considered.
With the emerging services over open industrial, scientic, and medical radio bands
(i.e., 2.4 and 5.8GHz) and the potential disruption over critical CBTC services, there
is an increasing pressure in the international community to reserve a frequency band
specically for radio-based urban rail systems. Such decision would help standardize
CBTC systems across the market and ensure availability for those critical systems.
Another challenge lies in systems with poor line-of-sight or spectrum/bandwidth
limitations. A larger than anticipated number of transponders may be required to
enhance the service. is is usually more of an issue with applying CBTC to existing
transit systems in tunnels that were not designed from the outset to support it. An
alternate method to improve system availability in tunnels is the use of leaky feeder
cable that, while having higher initial costs, achieves a more reliable radio link.
As a CBTC system is required to have high availability and, particularly, allows
for a graceful degradation, a secondary method of signaling might be provided to
ensure some level of nondegraded service upon partial or complete CBTC unavail-
ability. is is particularly relevant for browneld implementations (lines with an
already existing signaling system) where the infrastructure design cannot be con-
trolled and the coexistence with legacy systems is required, at least, temporarily.
Security is another big concern in CBTC systems. ere are many risks in CBTC
systems needed to be considered seriously due to the distinctive features of CBTC,
including open wireless transmission medium, nomadic trains, and lack of dedicated
infrastructure of security protection. erefore, in addition to the vulnerabilities and
threats of traditional wireless-based systems, the involvement of intelligence in CBTC
presents new security challenges. For many security issues, authentication is an impor-
tant requirement, which is crucial for integrity, condentiality, and nonrepudiation. In
addition, the experience in security of traditional wired and wireless networks indicates
the importance of multilevel protections because there are always some weak points
in the system, no matter what is used for prevention-based approaches (e.g., authen-
tication). is is especially true for CBTC systems, given the low physical security
autonomous functions of trains. To solve this problem, detection-based approaches
[e.g., intrusion detection systems (IDSs)], serving as the second wall of protection,
can eectively help identify malicious activities. Both prevention-based and detection-
based approaches need to be carefully studied for CBTC systems.
In addition, there is the probability of human error and improper application of
recovery procedures if the system becomes unavailable. erefore, it is important to
enhance the operator’s safety education and training, ensuring safe operation of trains.
1.5 Projects of CBTC Systems
CBTC technology has been (and is being) successfully implemented for a variety of
applications. Table 1.1 summarizes the main radio-based CBTC systems deployed
around the world as well as those ongoing projects being developed [4]. ey range
Introduction to Communications-Based Train Control ◾ 9
Table 1.1 Radio-Based CBTC Projects around the World
Country Location Line/System Supplier Solution Commissioning LoA
USA Washington Dulles
Airport
Dulles APM Thales SelTrac 2009 UTO
Seattle–Tacoma
Airport
Satellite Transit
System APM
Bombardier CITYFLO 650 2003 UTO
Sacramento
International
Airport
Sacramento APM Bombardier CITYFLO 650 2011 UTO
Massachusetts Bay
Transportation
Authority
Ashmont-
Mattapan High
Speed Line
Argenia SafeNet
CBTC
2014 STO
Canada Toronto Metro YUS line Alstom Urbalis 2013 STO
Ottawa Light Rail Confederation
Line
Thales SelTrac 2018 STO
Edmonton Light
Rail Transit
Capital Line
Metro Line
Thales SelTrac December 2014 DTO
China Beijing Metro 1, 2, 6, 9 Alstom Urbalis From 2008 to 2015 STO
Beijing Metro 4 Thales SelTrac 2009 STO
(Continued)
10 ◾ Advances in Communications-Based Train Control Systems
Table 1.1 (Continued) Radio-Based CBTC Projects around the World
Country Location Line/System Supplier Solution Commissioning LoA
Beijing Metro 8, 10 Siemens Trainguard
MT CBTC
2013 STO
Wuhan Metro 2, 4 Alstom Urbalis 2013 STO
Wuxi Metro 1, 2 Alstom Urbalis 2015 STO
Tianjin Metro 2, 3 Bombardier CITYFLO 650 2012 STO
Shanghai Metro 10, 12, 13, 16 Alstom Urbalis From 2010 to 2013 UTO and STO
Nanjing Metro Nanjing Airport
Rail Link
Thales SelTrac 2014 STO
Kunming Metro 1, 2 Alstom Urbalis 2013
Hong Kong MTRC Hong Kong APM Thales SelTrac 2014 UTO
Guangzhou Metro 6 Alstom Urbalis 2012 ATO
Taipei Metro Circular Ansaldo STS CBTC 2015 UTO
Singapore Singapore Metro North South Line Thales SelTrac 2015 UTO
Singapore Metro Downtown Line Invensys Sirius 2016 UTO
(Continued)
..................Content has been hidden....................

You can't read the all page of ebook, please click here login for view all page.
Reset
3.135.206.254