The global deployment of CBTC technology in mass transit transportation system is slowly but surely stepping into the infrastructure maintenance vehicles operation, raising the question about the automation level required for these specific rolling stock vehicles. Depending on the chosen automation levels, the effort level required to overcome the technical challenges requires proper assessment. Undertaking a multi-disciplinary criteria approach analysis with the right level of expertise at the early stages of the project will ensure that the investments will adequately meet the needs of the end users.

1. cbtc fitting strategies and challenges
for maintenance vehicles
by Sébastien Lacroix, SYSTRA Expert
www.systra.com

2. © SYSTRA 2016, COVER: © ISTOCK (EIRIK EVJEN)
Introduction
Due to their central role in modern cities mobility plans,
mass transit systems are under growing constraints to
meet higher service levels. The burden of these growing
constraints must be shared between the operation expec­
tations and the maintenance requirements. Often, the
Operator and the Maintainer of a given mass transit system
are two different entities, each of them having their own
interests and objectives, as set forth by the local authority.
A key element is the time window allocated to track
mainte­nance activities that results from a trade-off
between the passenger service level and the line infras­
tructure mainte­nance prerogatives.
In every railway transportations network, the infrastructure
maintenance activities rely mostly on dedicated vehicles
with characteristics quite different from the passenger
vehicles.
As CBTC applies mostly to urban environment, and unlike
mainline railways, the number of types of passenger
vehi­cles is usually limited to optimize the passenger service,
in contrast with the diversity of the maintenance vehicles
fleet which may be constituted of vehicles ranging from
track auscultation, multi tasks locomotives (flat cars,
cranes, track wash…), rail grinding/milling vehicles, down
to rail road vehicles.
The urban environment generates challenges to the
maintainer i.e. long commercial service period, if not 24/7,
with dense traffic, meaning little possession windows for
track maintenance activities.
In this strained environment, maintenance vehicle (“MVs”)
must be routed to the work zones and perform their
activity within optimized delays and at an acceptable level
of safety. Once MVs are at the work site, the safety of the
maintenance operation remains a concern that CBTC may
still address to some degree.
the global deployment of cbtc technology in mass transit transportation system
is slowly but surely stepping into the infrastructure maintenance vehicles operation,
raising the question about the automation level required for these specific rolling
stock vehicles. depending on the chosen automation levels, the effort level required
to overcome the technical challenges requires proper assessment. undertaking
a multi-disciplinary criteria approach analysis with the right level of expertise
at the early stages of the project will ensure that the investments will adequately
meet the needs of the end users.
cbtc fitting strategies and challenges
for maintenance vehicles
by Sébastien Lacroix, SYSTRA Expert
In its first part, this article intends to explain why the equip­
ment of MVs with CBTC technology is beneficial for the end
customer and to advise on the automation levels required.
The second part identifies some of the underlying technical
challenges of fitting maintenance vehicles. Then in the third
part, a list of criteria is feeding a more global top down
approach to pave the way for a cost-efficient analysis.
MVs fitting with CBTC:
is it necessary? And to
what level of automation?
The general trend in mass transit systems is to have less
equipment on the wayside, and to compensate these
materials reduction with intelligent control systems,
whether train centric or centralized. Practically, this race
to wayside equipment reduction is aiming towards the
suppression of wayside signaling and secondary detection.
Hence the need for making MVs participate in this evolving
concept of wayside equipment minimization by equipping
these MVs, and making them able to operate swiftly and
safely over a wayside striped off conventional signaling
devices.
The main two benefits for equipping MVs with CBTC are:
safety and performance.
MVs performance is directly related to passenger service
in the short run, but it surely has an overall effect on the
service quality in the long run: track maintenance interven­
tions can be postponed, but not forever.
Indeed, the main purposes of CBTC fitting is to ensure MV
routing to the work zone and back to the depot is perfor­
med at maximum design speed to offer the largest possible
maintenance dedicated time window to the maintainer.
2

3. The routing will be performed safely as the CBTC provides
at least an ATP function to the MVs and the CBTC may even
contribute, if so designed, to the safety of the MVs while
performing their maintenance tasks.
During the World Metro Congress 2016, the subject was
already tackled and a fruitful round table directed by
SYSTRA issued a preliminary guide to MVs automation
based on the MV families as shown in the table below.
In this particular workshop, the operation scenarios took
the following assumptions:
• GoA4 metro line,
• No signals for train separation control
(may have for routes indication),
• No Secondary Train Detection.
a maintenance plan analysis must identify when and how
often the mainte­nance activities can be accepted without
impacting beyond acceptable the passenger service: exclu­
sively at night out of commercial service, during weekends,
during low traffic hours, or even during low traffic periods
of the year where passenger transportation demand is
consis­tently low (for example: summer holidays).
The second task, taking the form of a bottom up approach,
is to analyze the fleet of MVs that is meant to intervene
and analyze how they can be equipped:
In the table 2 the following families of MVs are detailed:
Inspection (to measure) Track Work
Passenger
train type
Dedicated
MV
Multi-purpose
MVs
Special
MVs
Passenger
rolling
stock type
fitted with
underfloor
measuring
devices,
available for
commercial
service
MV fitted
with interior
and underfloor
devices
Ultrasound
inspection
Track geometry
Catenary
inspection,
gauge control,
wayside signaling
equipment check.
Track cleaning
(vacuum)
Locomotives
(Light diesel
or electric)
for towing:
Flat cars
Cranes
Cable laying
Welding
Track boring
(for civil work
inspection)
Rail Grinding
or Milling
Long rail
replacement
Rail road
vehicle
Table 2 - Families and types of Maintenance Vehicles
The table 2 shows the range and diversity of vehicles to be
taken into account by the signaling: dedicated autonomous
vehicles or trailers lead or surrounded by locomotives.
3
MV family MV type MVs’ Op. case
GoA Requested (x)
GoA Recommended (x) Comment
0 1 2 3 4
Inspection
(to measure)
Passengers’ train
equipped with
inspection tools
A X
B n.a.
C n.a.
Inspection
(to measure)
Dedicated MV
A X X X
GoA3 for regulation
GoA4 to be considered taking into account the
MV’s failure risks
B X X For maintenance traffic optimization
C X X For maintenance traffic optimization
Track Work
Light maint.
Transport train
A n.a.
B X X
C X X Not GoA2 for cost tech. complexity
Track Work Special train
A n.a.
B XX
C X X Not GoA2 for cost tech. complexity
Table 1 - Tentative guide to grades of automation
MV’s Operational cases:
A: Operation of MV within the revenue service,
B: Operation of MV behind the last passengers’ train,
C: Operation of MV outside the revenue service.
Another grade of automation not presented in table 1 is
sometimes used in some networks, this is an intermediate
grade between GoA 0 and GoA1: technically it is GoA0 but
the vital CBTC odometry function is relied upon, which im­
plies that MVs are equipped with a trainborne CBTC compu­
ter, odometry and CBTC radio, but without any interface to
the MVs braking and motoring systems: the only purpose
is to safely follow up the MVs routing and to trigger alarms
to the central operator in case of hazardous movement
detected, or even automatically trigger traction power sec­
tions cut-off over the area concerned by the alarm.
MVs CBTC fitting
equipment strategy
The first task to consider is the compromise between the
“Operator” for passenger service and the “Maintainer” for
infrastructure preventative and corrective maintenance:
based on the commercial service hours and traffic density,

4. 4
Track Geometry
inspection vehicle
in New York
A third task is to determine the range of movements that
are expected based on MVs missions:
The analysis will take into account the origins and desti­
nations of MVs interventions: the origin usually consists in
a depot dedicated to given line, but it may also be a depot
dedicated to MVs. In this case, the MVs shall operate on
different lines that may be equipped with different signa­
ling system leading to MVs equipped with various train­
borne CBTC or ATPs. The MVs movement origin may also
be siding tracks in order to reduce the routing time: in that
case, these siding tracks may require specific equipment
for the CBTC initialization.
Furthermore the maintenance activities on site may require
challenging functions for the CBTC:
• tracking splitting MVs at the beginning of the engineering
works, and the reassembling at the end of the theses
works,
• the range and nature of MVs movements (very slow speed,
running back and forth between any track locations) may
generate requirements for the odometry that are beyond
the passenger trains, performance needs.
Then comes the challenge of equipping this wide range
of MVs configurations with CBTC:
The dynamic performances, the maintenance consists
length and integrity, and their compatibility to an accurate
odometry: all these criteria are involved in the safe
management of the MVs movement.
The design choices for the MVs odometry is more proble­
matic than for passenger trains due the reduced number of
available reference axles, and the variable consist configu­
ration nature of the MVs vehicles or trailers. Hence more
equipment, such as optical devices, radar… are required to
complement the standard axle based odometry. Due to
technical constraints, most of the main CBTC equipment is
required to be installed on the same vehicle.
The wise option in terms of cost is to equip the MVs with
the same equipment as for the passenger trains: this is
preferable for investment cost as well as for maintenance
cost (interchangeability of spare parts). This equipment
shall fit all the different types of MVs. Then based on the
different dynamic performances of MVs fleet, two design
options are available for the CBTC configuration: taking the
worst case dynamic performances and apply to all the MVs,
or tune the CBTC to each MV type performance, which is
the preferred option for performance but it turns out more
costly.
Another alternative to limit costs with a less demanding
performance and safety level is to consider using RFID
technology instead of standard CBTC odometry to manage
MVs vital tracking. However, in this case, the operational
flexibility is reduced and the safety SIL level can barely
reach SIL2.
The ability to fit MVs with CBTC functions relies mostly
on the following elements:
1) Guaranteed emergency braking (worst case definition)
2) Available bulk space
3) Redundancy level required (linked to the 2 above points)
4) Migration issues: for green field, the design is made
more simple than equipping legacy MVs
Furthermore, the engineering costs are proportionally
increa­sed as the MVs’ fleet diversity grows.
All the above factors must be taken into account and analy­
zed in conjunction with the capital expenditure analysis.
A more global approach undertaken at preliminary design
and concept design stage is preferred to pinpoint the most
appropriate design.
Given the potential complexity of equipping the MVs fleet,
a top down approach taking into account a multi-criteria
analysis is recommended to spare consuming time and re­
sources. Such approach will most likely lead to identifying
some of the criteria shown hereafter.

5. 5
MVs CBTC
fitting strategy
especially if the MVs may evolve in the spatial or tempo­
ral vicinity of passenger trains. Furthermore, the driver’s
responsi­bility may not be sufficient to detect an unex­
pected split convoy in a timely manner.
• MV’s type, possibility of using passenger trains for track
supervision: as mentioned earlier in the article, MV’s
types impacts greatly the CBTC design choices. Passen­
ger trains refurbished and customized for maintenance
operations is an interesting choice to reduce cost while
benefiting from the dynamic performances of passenger
trains. Mixed traffic of MVs with passenger trains is then
facilitated.
• Wayside signals presence or not: with the generalization
of in cab signaling due to the CBTC development, the
wayside signals are left to cater for some degraded scena­
rios but can also be of use to manage MVs operations, as
well as protect pedestrian staff operation. These signals
may include spot ATP protection (AWS, TPWS,) easily
adaptable to MVs if the signaling sections are compatible
with the worst MVs braking performances. The reason
for equipping MVs with CBTC in case of wayside signals
presence is to improve the running performances and
overall operation safety.
• Interoperability issue of having different CBTCs on the
same network: in this case, the CBTC fitting MV strategy
needs to be taken to the next level, using a more global
approach consistent with the long term vision of the
CBTC procurement strategy of the network. A multi-
criteria technical economic analysis taking into account
the maintenance and operation target will determine the
best CBTC fitting strategy.
• Infrastructure maintenance strategy: maintenance plan,
activities scheduling, type of allowed movements with
respect to commercial operation.
The above subjects give an insight of the multi-disciplinary
complexity of the MVs subject. Each use case shall be
analyzed through a multi-criteria matrix to be initiated
during the earliest stages of the project, obviously earlier
than the tender stage, in order to provide a technical
solution consistent with the use case.
The figure above, based on the established criteria
already identified during the Smart Metro Congress 2016
workshop reminds the main criteria to take into account
in the MVs CBTC fitting analysis. Based on these criteria,
further considerations are mentioned here under:
• Regulations Laws, MVs safety management, staff pro-
tection, which may make the ATP functions mandatory:
for example in Paris urban network, the national railway
regulation applies, any MVs that is allowed to run at a
speed greater than 60kph must be fit with ATP. In further
compliance to this regulation, the ATP must be adapted
to the target environment of the MV, i.e. in a dense urban
environment, the CBTC is highly recommended.
• Secondary train detection, having it or not: the gene­
ral trend for secondary detection (axle counters, track
circuits, optical barriers…) is to be reduced to the strict
minimum for degraded operation or even not to have it
for new lines. In the absence of secondary train detec­
tion, MVs fitting with CTBTC is mandatory. Where spare
secondary detection is implemented, CBTC fitting does
improve the work zones density by reducing the track
possession requirements, and the routing time to and
from the work site.
• 24/7 operation and its impact on MVs activities opera-
tion window: requires a high level of safety imposed by
the vicinity of MVs circulations and activities with passen­
ger trains, as well as a high level of performance to limit
the impact on the passenger service. CBTC fitting shall be
designed in the light of these 2 requirements.
• Track possession management and traction power; how
movement authorities and traction power are set: CBTC
contribution to possessions management is signi­ficant as
it manages train movement authorities, therefore being
able to offer some level of staff protection within the
work zones. Another potential role that can be attri­buted
to the CBTC is the traction power distribution control
to assist the operator and maintainer in the safe mana­
gement of traction power sections during maintenance
activities.
• MVs integrity check, having such function impacts MVs
safe traffic supervision: the nature of MVs (multi-consist
operation, diverse rolling stock…) makes the integrity
check even more important than the passenger vehicles,
Regulations Laws
Secondary Train Detection
24/7 operation
Track possession
management
Infrastructure
maintenance strategy
Interoperability Issues
Wayside signals:
with or without
MV’s rolling stock type MV’s integrity check

6. 6
© ISTOCK(CHALABALA)
Conclusion
safe bet to expect that self-operating main­
tenance vehicles will progressively meet the
ever growing expectations of mass transit
service levels.
SYSTRA is already involved in large scale
CBTC projects with ambitious CBTC
target for the management of maintenance
vehicles: this is just one of the numerous
fields where SYSTRA can provide its exper­
tise with its global vision of the customer’s
interests.
This huge interdependency of criteria requi­
res a system wide expertise to draw a line
in the trade-off of the constraints and bene­
fits: there are no perfect technical solution,
no generic solution. This expertise activity
is an investment in the early stage of the
project to ensure that the MVs management
will address the maintainer needs and save
money to all involved parties.
Looking towards the future and considering
the latest progress in other industries, it is a