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cbtc fitting strategies and challenges for maintenance vehiclesby Sébastien Lacroix, SYSTRA Expert
www.systra.com
© SYSTRA 2016, COVER: © ISTOCK (EIRIK EVJEN)
IntroductionDue 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 expectations 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 mainte nance activities that results from a tradeoff between the passenger service level and the line infrastructure mainte nance 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 vehi cles 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 vehiclesby Sébastien Lacroix, SYSTRA Expert
In its first part, this article intends to explain why the equipment 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 costefficient 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 interventions 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 performed at maximum design speed to offer the largest possible maintenance dedicated time window to the maintainer.
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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 mainte nance activities can be accepted without impacting beyond acceptable the passenger service: exclusively 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 consis tently 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 carsCranesCable 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.
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MV family MV type MVs’ Op. caseGoA Requested (x)
GoA Recommended (x) Comment0 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 XGoA3 for regulationGoA4 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 automationMV’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 implies that MVs are equipped with a trainborne CBTC computer, 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 sections cutoff over the area concerned by the alarm.
MVs CBTC fitting equipment strategyThe 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,
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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 destinations 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 signaling system leading to MVs equipped with various trainborne 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 problematic than for passenger trains due the reduced number of available reference axles, and the variable consist configuration 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 increa sed as the MVs’ fleet diversity grows.
All the above factors must be taken into account and analyzed 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 multicriteria analysis is recommended to spare consuming time and resources. Such approach will most likely lead to identifying some of the criteria shown hereafter.
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MVs CBTC fitting strategy
especially if the MVs may evolve in the spatial or temporal vicinity of passenger trains. Furthermore, the driver’s responsi bility may not be sufficient to detect an unexpected 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. Passenger 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 scenarios 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 multicriteria 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 multidisciplinary complexity of the MVs subject. Each use case shall be analyzed through a multicriteria 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 general 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 detection, 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 passenger 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 signi ficant 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 attri buted to the CBTC is the traction power distribution control to assist the operator and maintainer in the safe management of traction power sections during maintenance activities.
• MVs integrity check, having such function impacts MVs safe traffic supervision: the nature of MVs (multiconsist 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
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Conclusion
safe bet to expect that selfoperating maintenance 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 expertise with its global vision of the customer’s interests.
This huge interdependency of criteria requires a system wide expertise to draw a line in the tradeoff of the constraints and benefits: 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
