20 ◾ Advances in Communications-Based Train Control Systems
previous tests and software development. ere is no transportation department
to interface with during testing, which is usually a very time-consuming interface.
Another advantage is that the interfaced system may also be under development
so interface design issues can be resolved by changing the CBTC or the other sys-
tems. New lines are often for new or recent transit systems which are more likely
to embrace new technology and accept the method of testing recommended by the
CBTC suppliers.
e disadvantage of greeneld projects is that the signaling system is the last
part of a complete transportation system dependent on other systems. e result
is that the signaling project is planned with a very compressed schedule without
any slack in order to absorb previous system delays. Another diculty for proj-
ects on new lines is that the other systems, which also require track access, may
not be working properly during the CBTC tests. In particular, the rolling stock
may be ready for CBTC tests but not for revenue operations, and the remaining
rolling stock issues may aect CBTC tests if a train becomes stranded during
testing.
2.3.2 Migrating an Existing Line: Browneld Project
In large cities where the railway infrastructure was created decades ago, the cost
of building a new line is very high and the time to create a new line is very long.
Transit agencies prefer improving the capacity of existing lines in only a few years.
Buying new trains with better performance and more passenger space is a possibil-
ity to improve the line capacity. In addition to or instead of buying new trains, the
transit agency might decide to upgrade to CBTC technology to increase capacity
by minimizing the headway between trains. Upgrading the signaling system of an
existing line is referred as a browneld project.
On a migration project, the biggest challenge is to get sucient track access to
install and test the new system while maintaining revenue service operation [2,3].
During revenue service hours, tracks are used to transport passengers, and during
o hours or during nonpeak hours, maintenance actions to support the revenue
service operation are performed. Installation and testing must be integrated with
the maintenance schedule of the existing transportation system for the duration of
the eld activities of the CBTC project.
Transit agencies may plan to convert only one line or their entire system to
CBTC. Several migration approaches, which aect testing strategy, have been
used. One approach is to deploy CBTC on a line that is not very busy in order
to learn about the system and to minimize the risk of deploying CBTC on a
more busy line, usually under strong political scrutiny. Another approach is to
directly use CBTC on the busiest line because the capacity needs to be improved
as quickly as possible. ose browneld projects on busy lines have the highest
planning risk and need both an experienced CBTC supplier and a transit agency
familiar with CBTC. Some of the very ambitious projects have failed or were
Testing Communications-Based Train Control ◾ 21
considerably delayed, lasting more than 10 years. Finally, another approach is to
have mega projects where all lines are upgraded at the same time using one or
several suppliers, where test results on the rst line may be used for the other lines
to cut the total test time.
2.4 CBTC Architecture
e CBTC system considered in the this chapter is described in Refs. [4–6]. It is
composed of four subsystems:
◾ Carborne Controller (CC). The CC, also called OnBoard Controller Unit
(OBCU), is located on board the train. It is responsible for determining
the train speed, the train location, and the enforcement of the speed limit
based on the movement authority limit (MAL).
◾ Zone controller (ZC). e ZCs are located in the technical rooms. ey are
responsible for calculating and providing the MAL to the CC based on
theinformation received from the trains and from other subsystems such as
the interlocking. ere are several ZCs per project to provide coverage for the
full line. ey exchange information with the onboard controllers in their ter-
ritory and controll, directly or through an external signal system, eld equip-
ment such as switches.
◾ ATS system. e ATS system regulates train operations. It includes a human–
machine interface with the operators at the Operations Control Center
(OCC).
◾ Data communication system (DCS). e DCS includes both the wayside com-
munication network and the train to wayside communication system.
2.5 Principles of CBTC Testing
2.5.1 Reuse as Much as Possible from Previous Projects
ere are only a few CBTC suppliers around the world, and most of them havebeen
developing CBTC technology over the past decades. CBTC suppliers have dier-
ent CBTC products depending on the features such as driverless operation. eir
systems are the result of improvements over the years using feedback from previous
projects regarding train operation, lessons learned on the deployment of the system,
and advances in technology such as the IEEE 802.11 standard WiFi [7]. When
a new product is developed, CBTC suppliers reuse the current version of their
product, both the hardware and the software, and include improvements. e new
CBTC product is then deployed on several transit properties in parallel until the
next generation. It is common that the new product is developed for a large project
22 ◾ Advances in Communications-Based Train Control Systems
identied as a development project. Transit agencies want a service-proven technol-
ogy, which takes into account the latest technology with plans to customize it.
is strategy of using the same product for several projects has two direct
impacts on the tests of CBTC:
◾ e rst project of a new CBTC product is much more dicult than the
previous projects done by the supplier. After the rst project, other projects
benet from the work already done, and only specic features of the follow-
ing projects are challenges.
◾ Previous development and test results can be reused. Because CBTC is a very
complex and large system, reusing as much as possible the same hardware and
software while adding improvement is a must. Core functions of CBTC have
been the same for decades. e product team of the CBTC suppliers is in
charge of performing low-level tests transparent to the transit agency. Items
that can be reused are not only the software of core functions but also the
factory setup, including simulators, and documentation, such as test proce-
dure or safety analysis. Transit agencies expect that the CBTC supplier reuses
previous projects to develop the system on their property, but test results from
another projects cannot be used. e use of other project is valid for CBTC
supplier internal purposes only.
2.5.2 Test in Factory as Much as Possible
In order to minimize eld tests that require track access with far more resources
than factory tests, a complete set of factory tests must be performed before using
the software on-site. CBTC systems allow for intense factory testing using real
equipment interfaced with environment simulators. Almost all functions of the
CBTC can and should be tested in the factory environment in order to verify the
system and detect most of the anomalies. Integration between the CBTC supplier
factory and the eld team is key for successful eld tests.
2.5.3 Test All Safety-Related Items
All functions related to safety, such as enforcement of speed limit, must be tested in
the factory and/or in the eld intensively. is statement is also valid for eld data
such as the position of platforms along the track. Tests of safety functions are used
as checks which provide a high-level condence about the system before revenue
service. In addition to completing the safety certication process, CBTC suppliers
and authorities having jurisdiction ensure that all safety functions are completely
tested before authorizing revenue service.
Functions not related to safety should be tested in order to verify proper operation
and minimize impacts on revenue service, but the intensity of tests for nonvital func-
tions should be optimized to avoid unnecessary delays to the revenue service operation.
Testing Communications-Based Train Control ◾ 23
2.6 Environmental Tests
At the end of the design and before starting the production of the equipment,
CBTC equipment is subject to its rst set of tests: environmental tests. e dierent
types of environmental tests are as follows:
◾ ElectroMagnetic Compatibility (EMC) tests
◾ Climatic condition tests
◾ Mechanical condition tests
◾ Abrasive condition tests
Transit agencies and CBTC suppliers establish an environmental test plan to agree
on what equipment belongs to each category. e category of the equipment is
used to dene the test requirements as described in the appropriate test standard.
In addition, any specic condition of a particular railroad environment is identied
based on eld’s measurements and tested against.
A common practice in CBTC projects is to accept test results performed by
the supplier during their product testing or for another project. is is the only
time where test results from other projects may be considered. Dierence between
the equipment tested on other projects and the equipment for the current project
should be analyzed very carefully during this process.
2.6.1 EMC Tests
e goal of the EMC laboratory qualication tests is to verify the level of electro-
magnetic immunity, that is, susceptibility, and the electromagnetic emissions of the
CBTC equipment. ese tests are performed in a certied laboratory. As described
in [8], which summarizes the EMC activities in CBTC projects, there are two major
standards for this activity: (1) CENELEC (European Committee for Electrotechnical
Standardization) Standard EN50121 Railway Applications Electromagnetic
Compatibility [9] and (2) International Electro-Technical Commission IEC 62236
[10] with the same title. e standard’s criteria may need to be adapted to take into
account the specicities of CBTC in a railroad environment. For instance, some
CBTC radios use the 5.8GHz frequency so the test should be performed up to
6GHz instead of the 1GHz as currently required in the standards.
2.6.2 Climatic Conditions
Climatic condition verications are related to extreme temperature and humidity
tests. Cycles of very cold then ambient temperatures and cycles of very hot then
ambient temperatures are tested as per MIL-STD-810F Test Method standard for
Environmental Engineering Considerations and Laboratory Tests [11]. Also, cycles of
dry and humidity environments are tested as per [11].
24 ◾ Advances in Communications-Based Train Control Systems
2.6.3 Mechanical Conditions
Mechanical condition verications are related to vibration and mechanical shock
tests. Standards used are IEC 61373 for rolling stock equipment [12], EN 60068-
2-64on vibration tests [13], and EN 60068-2-27on shock tests [14] for wayside
equipment. It is common that vibration tests help reveal issues with the mechanical
design, and therefore among the environmental tests, the vibration test is one of the
most important.
2.6.4 Abrasive Conditions
Abrasive conditions are verifying dust and water protections. e size of dust akes
and the amount of water are tested as per IEC 60529 Degree of Protection provided
by enclosures [15] depending on the IP code claimed for the equipment. Another
type of abrasive testing is the salt fog that can be tested as per [11]. is test is
especially important for roadway equipment which is subject to the most severe
conditions.
2.7 First Article Conguration Inspection
First Article Conguration Inspection (FACI) is the rst check using real equip-
ment by the transit agency that happens in CBTC projects. is activity happens
toward the end of the design phase of the project after the equipment has been
designed on paper and before starting mass production. e FACI’s goal is to verify
that production hardware complies with design conguration, drawings, and soft-
ware design. It provides a means to verify that all documentation is ready for mass
production. It also includes the evaluations of maintainability and accessibility.
is activity typically takes place at the point of assembly after completion of envi-
ronmental qualication tests of the prototypes.
2.8 Factory Tests
Verication and validation, as described in the International Council on Systems
Engineering handbook [16], should be done as much as possible in the factory.
CBTC systems allow this type of intensive factory testing and only a few parts can-
not be completely tested in the factory. For instance, the interface with the rolling
stock cannot be completely tested in the factory. Other parts that cannot be tested
are the radio coverage and the database for eld data. Functions related to the man-
agement of a large number of trains are also dicult to test at the system level.
Despite the use of powerful tools such as integrated system factory setup and simu-
lators, it is frequent that anomalies that could have been discovered in the platform
are discovered on-site.
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