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DELIVERABLE D0602. FINAL CONSOLIDATED REPORT - CHAPTER 2 Related Milestone CONTRACT N° 031312 PROJECT N° FP6-31312 ACRONYM URBAN TRACK TITLE Urban Rail Transport PROJECT START DATE September 1, 2006 DURATION 48 months Subproject SP6 SP6 Work Package WP6.2 Consolidation Technical consolidation report on all validation results (Chapter 2) Written by Yves Amsler and Caroline Hoogendoorn UITP
Date of issue of this report 15/11/2010 PROJECT CO-ORDINATOR Dynamics, Structures & Systems International D2S BE PARTNERS Société des Transports Intercommunaux de Bruxelles STIB BE Alstom Transport Systems ALSTOM FR Bremen Strassenbahn AG BSAG DE Composite Damping Materials CDM BE Die Ingenieurswerkstatt DI DE Institut für Agrar- und Stadtökologische Projekte an ASP DE der Humboldt Universität zu Berlin Tecnologia e Investigacion Ferriaria INECO-TIFSA ES Institut National de Recherche sur les Transports & INRETS FR leur Sécurité Institut National des Sciences Appliquées de Lyon INSA-CNRS FR Ferrocarriles Andaluces FA-DGT ES Alfa Products & Technologies APT BE Autre Porte Technique Global GLOBAL PH Politecnico di Milano POLIMI IT Régie Autonome des Transports Parisiens RATP FR Project funded by the Studiengesellschaft für Unterirdische Verkehrsanlagen STUVA DE European Community under Stellenbosch University SU ZA the Ferrocarril Metropolita de Barcelona TMB ES SIXTH FRAMEWORK Transport Technology Consult Karlsruhe TTK DE PROGRAMME PRIORITY 6 Université Catholique de Louvain UCL BE Sustainable development, Universiteit Hasselt UHASSELT BE global change & ecosystems International Association of Public Transport UITP BE Union of European Railway Industries UNIFE BE Verkehrsbetriebe Karlsruhe VBK DE Fritsch Chiari & Partner FCP AT MetrodeMadrid MDM ES Frateur de Pourcq FDP BE
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TABLEOFCONTENTS
2. Cost effective track maintenance, renewal & refurbishment methods (SP2) ...... 4 2.1. New low cost renewal and refurbishment methods: Description of tracks with regard to renewal and improvement possibilities (WP2.1, developed by STUVA) ...... 4 2.1.1. Basic Rules for efficient low-cost-criteria...... 4 2.1.2. Recommendations for Refurbishment and renewal of single track elements ...... 5 2.1.2.1. Rails...... 5 2.1.2.2. Switches ...... 5 2.1.2.3. Rail Fastenings...... 6 2.1.2.4. Sleepers ...... 6 2.1.3. Recommendations for packing cleaning and recycling of ballast ...... 7 2.1.4. Recommendations for track design...... 7 2.1.4.1. Optimisation of design conditions...... 7 2.1.4.2. Change from ballast track to slab track...... 7 2.1.4.3. Specific design criteria for concrete slabs ...... 8 2.1.4.4. Specific design criteria for tracks on steel viaducts...... 8 2.1.4.5. Special measures for track transitions...... 8 2.1.4.6. Selection of the most efficient solution ...... 9 2.1.5. Recommendations for noise and vibration protection...... 9 2.1.5.1. Observation of basic rules...... 9 2.1.5.2. Avoidance of over-design...... 9 2.1.5.3. Adoption to local situation ...... 10 2.1.5.4. Combined measures for ballast tracks...... 10 2.1.5.5. Additional noise reducing measures on slab tracks...... 10 2.1.5.6. Rail grinding important for noise reduction...... 10 2.1.5.7. Curve-squeal mitigation ...... 11 2.1.6. Recommendations for fire and rescue issues...... 11 2.1.6.1. Improved self rescue requirements...... 11 2.1.6.2. Horizontal exit/entry conditions ...... 11 2.1.6.3. Avoidance of toxic gases...... 11 2.1.7. Recommendations for occupational safety and health considerations...... 12 2.1.7.1. Hazards and provisions...... 12 2.1.7.2. General measures to minimise hazards...... 12 2.1.7.3. Specific safety measures on bridges with embedded or segregated tracks...... 13 2.1.7.4. Specific measures in tunnels and on viaducts...... 13 2.1.7.5. Specific measures for driverless metros...... 13 2.1.8. Tests on a test circuit and hydro-pulse-facility for embedded tracks ...... 14 2.1.8.1. Description of the test facilities...... 15 2.1.8.2. Description of the test bodies embedded in road surfaces...... 16 2.1.8.3. Conducting the tests on the test circuit...... 17 2.1.8.4. Conclusion...... 21
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2.2. Optimal maintenance methodology (WP2.2)...... 23 2.2.1. Visual inspection & maintenance (WP2.2.1, developed by FCP) ...... 23 2.2.1.1. Introduction...... 23 2.2.1.2. Strategy used and description of the methods...... 23 2.2.1.3. Results...... 23 2.2.1.4. Conclusions...... 26 2.2.1.5. Bibliography ...... 27 2.2.2. Predictive and preventive maintenance of metro tracks (WP2.2.2, developed by INSA, INRETS and D2S)...... 28 2.2.2.1. Understanding rail lubrication impact (WP2.2.2a, developed by INSA)...... 28 Conclusions...... 29 2.2.2.2. Solving the problem of rail track reliability estimation (WP2.2.2a, developed by INRETS)...... 34 Background ...... 34 Probabilistics Graphical Models ...... 35 Definitions...... 35 CPD parameters learning...... 35 Inference in PGMs...... 36 Dynamic probabilistic graphical models...... 36 Introduction of the Graphical Duration Models...... 38 Qualitative definition...... 38 CPDs definition...... 39 Reliability analysis using GDM...... 41 Basic definitions ...... 41 Reliability...... 41 Failure rate...... 42 Mean Time To Failure (MTTF)...... 42 Conclusions...... 42 Estimation method...... 43 Application to track reliability estimation...... 45 Variables definition...... 45 CPDs learning ...... 46 Results...... 47 Conclusions and Perspectives...... 48 2.3. Advanced maintenance strategies (WP2.3 developed by TTK)...... 50 2.3.1. Introduction...... 50 2.3.2. Methodology...... 51 2.3.3. Conclusions...... 53 General tendencies regarding track management...... 53
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2. COST EFFECTIVE TRACK MAINTENANCE, RENEWAL & REFURBISHMENT METHODS (SP2)
The sub-project SP2 focuses on existing tracks and deals with cost effective track maintenance, renewal & refurbishment methods. It covers the following sub-packages:
new low cost renewal and refurbishment methods for track (WP2.1) optimal maintenance methodology (WP2.2), divided in three sub-packages: o visual inspection and maintenance (WP2.2.1); o predictive and preventive maintenance of metro tracks (WP2.2.2); o preventive maintenance of embedded tram tracks (WP2.2.3)
advanced maintenance strategies (WP2.3).
Recommendations from this chapter are validated in chapter 3 (chapter 3.5, Bremen) and are an input for chapter 4 on LCC and chapter 5 on definition of functional requirements and functional specifications for tram and metro track.
2.1. NEW LOW COST RENEWAL AND REFURBISHMENT METHODS: DESCRIPTION OF TRACKS WITH REGARD TO RENEWAL AND IMPROVEMENT POSSIBILITIES (WP2.1, DEVELOPED BY STUVA)
The recommendations for tunnels and viaducts exemplarily are shown in the following. In principle similar recommendations were worked out also for the two other kinds of tracks (tracks with separate right of way on the surface and embedded in roads). Typical tracks in roads were examined with regard to duration long-lastingness at a test facility (circuit) in the STUVA. Green tracks were also checked with regard to traffic ability due to vehicles of the police, the fire brigade and of ambulances at this test facility. These results are summarized in report D2.11 (see Chapter 2.1.8).
The validation site has been Bremen, Germany, see chapter 3.4 and 3.16.
2.1.1. Basic Rules for efficient low-cost-criteria
The following basic rules for a definition of efficient low-cost-criteria should be observed:
There can be no “one-design-fits-all” solution for urban tracks. An optimal and economical track design is always adapted to exactly defined local conditions. Above all, low cost solutions shall not lead to poor quality solutions.
Therefore “efficient low-cost” can only mean: “select under given framework and quality conditions the appropriate technical solution, which leads to the lowest possible costs over the entire lifetime of the system (LCC), while considering all mentioned individual cost factors from planning and constructing until disposal.”
The following recommendations therefore offer for most conditions and interdependencies a “modular system” of solutions with their economical aspects.
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2.1.2. Recommendations for Refurbishment and renewal of single track elements
2.1.2.1. Rails
Removed vignole rails in an open superstructure should always be examined for re-use after reconditioning (rail realignment or re-profiling). Such reconditioned rails may be used in track categories/sections with lesser operating loads or lower running speeds (e. g. outer branches of lines; yard tracks etc.). Reconditioning of vignole rails normally creates economic advantages compared with the use of new rails.
Because replacement of rails in open tracks normally is relatively easy to practice, other rail refurbishing methods such as rail resurfacing by welding or the use of high-grade steel qualities for rails (e. g. head hardened rails) in most cases is not an economic solution in tunnels and on viaducts. Only when (e.g. as often practised on bridges) the rails are embedded in the structure/floor slab, these measures should be taken into account. In such cases extended rail service life can lead to lower LCC-costs compared to the exchange of rails (for further details see Deliverable D 2.3 “Embedded Tracks”).
2.1.2.2. Switches
Switches are subject to heavy stress and high levels of wear. On economic reasons, the number of switches should be limited to the absolute necessary requirements for a flexible train operation especially in case of failures or breakdowns. Complex systems (e. g. double switches) procure high maintenance costs and should therefore be avoided as far as possible. Standard switch solutions using uniform components should be selected with priority and for low cost reasons.
Consideration of both, technical and economical criteria, suggests observing the following rules for switches in all track types:
The rail profile of a switch being installed should correspond to that of the connecting tracks.
Switches with a larger diverging track radius are longer and more expensive, but allow vehicles to travel at higher speeds on the diverging track and are less susceptible to wear. Consequently, switches with a larger radius should be used if they are to be passed through frequently by scheduled services.
Where possible, vehicles should be able to cross-branching switches in main lines on the diverging track at the speed permitted on the adjacent track.
To avoid mutual disruptions during installation and subsequent replacement works, the switches should be configured independently of each other and not 'overlap' with sleepers on adjacent tracks.
Switch tongues of vignole rails in open tracks should be exchanged rather than reconditioned by welding, because the open position allows that the tongue blade can be replaced easily and quickly, without interrupting train service.
Because switches are highly complex, their installation, repair, or exchange on site is expensive and labour intensive, especially in tunnels and on bridges. Pre-assembling of switches in the factory with extreme precision and in parts, enabling them to be installed on site as fast as possible, but still
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transportable, and with minimal operational disruptions is therefore a precondition for efficient low cost solutions.
To optimize switch maintenance it is recommended to install interdisciplinary maintenance teams. The aim is a replacement of preventive or corrective maintenance with a condition-driven approach that is only applied when and where necessary. This leads to the most economic solution. Full replacing of switches is very expensive and time- and labour intensive. It should be avoided as far as possible.
2.1.2.3. Rail Fastenings
The kind of rail fastening system used for specific applications influences remarkably track’s static stiffness, precision of rail alignment, load distribution, stray current insulation, noise and vibration emission and therewith travel comfort. Because these requirements gain increased importance in urban transport, indirect rail fastening systems should be preferred today. These fasteners offer the possibility to adapt the insulation and deflection criteria of the track bed within given limits to specific local demands, which is of high economic importance with reference to refurbishment and renewal works.
Especially for urban railway tracks, it is of high importance today that the selected rail fastening system consists of the fewest possible parts and allows pre-assembling (e.g. on sleepers or on prefabricated concrete elements) before being delivered to the place of installation. This enhances the quality of construction and reduces on site assembly time and costs, especially for use with slab tracks.
Whenever in tunnels and on bridges the limit values for noise and vibration emission can be reached by specific rail fastening designs, this has proved the most economic solution compared with all other measures. Continuous, elastic rail fastenings (perhaps based on new and successful solutions for embedded rails) should be taken into account also for tunnels and bridges.
For service and economic reasons, the exchange of rails and rail fasteners should be coordinated and realized at the same time wherever possible.
2.1.2.4. Sleepers
Because of increasing legal restrictions for the use of impregnating materials and also for economic reasons (LCC), wood sleepers should be replaced by pre-stressed reinforced concrete sleepers, whenever refurbishment or renewal measures are necessary in urban transport. Especially in tunnels, this additionally reduces fire risks and release of toxic gases.
The lower axle loads in urban transport make lighter pre-stressed concrete sleepers sufficient. For example, the use of bi-block sleepers has proved technically and economically advantageous, preferably in conjunction with renewal as slab track.
Solutions with polymer concrete sleepers, Y-steel sleepers and plastic sleepers (PUR) embedded in concrete are exceptions in urban transport so far. The latter may gain some further importance with respect to the reduction of noise and vibrations and better electrical insulation.
Replaced reinforced concrete sleepers should always be examined for re-use. Quality tests decide, whether they can be used in normal tracks or in sections with lower loads. Reconditioning of sleepers creates ecologic and economic advantages compared with the use of new sleepers.
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2.1.3. Recommendations for packing cleaning and recycling of ballast
As the ballast bed grows increasingly contaminated in course of time, the pressure dispersion angle below the sleeper decreases, which can lead to uneven loads on the track formation and thereby, in certain circumstances, to shifting and settling. Besides that, the ballast bed loses elasticity and permeability. As a result, regular inspection of the track and cleaning of the ballast (if necessary) are required.
Because packing (tamping) is one cause of destruction of ballast grain and particle disintegration the number of packing operations is limited before ballast cleaning or replacing is needed. Tamping can raise the rail level. This also can be a reason for bedding cleaning. Bedding cleaning is normally required after about 35 years.
In tunnels, additional safety aspects need to be considered. Light waste materials (such as leaves, paper and so on) are scattered by draughts into the wider areas just before stations or into any niches, where they settle and become a fire threat. Their regular removal e. g. with suction machines is thus required for fire protection reasons.
In urban public transport systems, the dense network of stops and frequent halting at signals (due to both railway signals and traffic lights, etc. on roads), the risks of pollution of ballast (e. g. by fuel and lubricants) are far higher than on the railways in general. This can lead to a higher intensity and frequency of cleaning and thus also impacts on profitability.
Almost all regulations in force today recommend recycling of contaminated ballast. In urban public systems, the cleaning of ballast in mobile facilities close to the construction site and the re-use as lower ballast layer on renewed tracks has proved the most economical procedure. However: Several environmental rules must be observed when disposing, cleaning and re-using ballast with (perhaps) restricted application.
2.1.4. Recommendations for track design
2.1.4.1. Optimisation of design conditions
Urban railway tracks in tunnels and on viaducts are completely independent of other traffic (not always on bridges). The substructure is the tunnel or viaduct construction, which form a solid (normally concrete) and settlement-free base for the superstructure of the track. These conditions are ideal and allow a relatively free choice of track design. This situation should be used to optimize the design technically and economically to the specific conditions of the particular application.
2.1.4.2. Change from ballast track to slab track
In tunnels and on bridges a change from ballast track to slab track is recommended, whenever renewal or refurbishment measures are necessary. This has especially two reasons:
Due to narrow spaces, repair and maintenance works are difficult to carry out and should therefore be limited as far as possible; On escape and rescue reasons in case of fire a solid track bed with even surface is of high importance.
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Under these circumstances, the higher investment costs of slab tracks are justified especially in tunnels and on bridges.
When using floating-slab-systems, along term effective and easily accessible drainage is of crucial importance for the long term functioning, therewith avoiding water accumulation and sintering effects in the joints with the elastomeric layer.
2.1.4.3. Specific design criteria for concrete slabs
When using concrete slab tracks or floating-slab-systems in tunnels and on bridges important design criteria have to be observed:
The slab always has to be separated from the substructure by an elastic layer (reasons: separate freedom to move; vibration protection). To avoid longitudinal sliding of the slab when breaking (of trains), special anti-shear-devices (such as cams or anchors) need to be installed at pre-defined places of the structure.
Protection against stray currents of any reinforced concrete parts is important to observe, e. g. by interconnection of the reinforcement mats of the individual concrete elements.
When using floating-slab-systems, along term effective and easily accessible drainage is of crucial importance for the long term functioning, therewith avoiding water accumulation and sintering effects in the joints with the elastomeric layer.
The observation of these criteria is strongly recommended, because they are of high importance for the durability of the structure (avoidance of damages) and thereby influences life-cycle-cost remarkably.
2.1.4.4. Specific design criteria for tracks on steel viaducts
A new and effective solution for steel viaducts is the direct placement of rails on the steel structure (e.g. on longitudinal beams) by highly elastic rail fasteners. It is of crucial importance in such cases, to realize possible longitudinal movements of the rail (e.g. sliding on Teflon elements), independently from the viaduct structure to avoid uncontrolled load distribution. Only on exactly defined and placed fixed support points the longitudinal forces should be distributed (controlled) via the bridge structure to the foundation.
Corrosion protection measures connected with refurbishment works should on economic reasons be adjusted to the individual extend of damages. Besides the application of specific coatings, the electric interconnection of the different steel elements of the viaduct (avoidance of stray current corrosion) and an effective drainage of the steel structure (avoidance of water accumulation) has to be observed.
2.1.4.5. Special measures for track transitions
Track transitions from both slab tracks to ballast superstructures and from engineering structures (tunnel, bridge) to earth structures need specific measures. It is recommended to focus special attention to these sections of a track way.
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Especially the areas of engineering and earth structures may differ starkly in subsidence behaviour (danger of deformation and/or formation of ledges). An adoption in rigidity is therefore needed in the transition sections, e. g. by graduated cementing of the critical backfill areas or by using a transition slab.
Transitions from one track type to another should not take place in curves and not come directly after switches and crossings.
2.1.4.6. Selection of the most efficient solution
The “most efficient” solution for a railway track must always observe technical and economical aspects as well as local requirements and the interests of line-side residents (e.g. adjacent to viaducts). One-sided optimisation cannot fulfil the demands of the train operator and other involved parties.
The planning engineer’s knowledge of the cost relations for different track designs is (independent from real investment cost values) of high importance, because this can lead to the technically and economically most efficient solution for exactly defined local framework conditions.
Of special importance for complete renewal of public rail tracks (especially on viaducts and bridges) in densely build up urban areas are henceforth:
The early participation of all involved parties; A perfect neutral (and external) project management; An open minded and transparent public relation work by humanly and professionally competent persons, placed directly on the building site; High quality contractors; The exact observation of (mostly) tough time schedules.
Only such “joint efforts” can result in an overall success of the measure.
2.1.5. Recommendations for noise and vibration protection
2.1.5.1. Observation of basic rules
To reduce vibration effects it is of high importance to observe two basic rules:
The natural frequencies of the ceilings in the (line adjacent) buildings should be measured. The track bed should have another natural frequency to avoid resonance effects in the ceilings.
The support point spacing of the rail in the track bed should not be a multiple of the distance between the wheels of the vehicle, to avoid any “build up” of vibrations in the wheel set.
These rules lead to the following recommendation: track bed design should always be adapted to vehicle and design of adjacent buildings to reach best possible vibration abatement effects.
2.1.5.2. Avoidance of over-design
For urban railway tracks in tunnels and on bridges, noise and vibration protection is a feature, which gains growing importance. It is therefore a cause for renewing or refurbishment works. But the technical
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solutions show a great variety of possibilities and differ largely in costs. Therefore, the measures should be strictly adjusted to the real demands of the given situation on different track sections. These may change in the course of a line. The tendency to the use of one single-track design (e.g. floating-slab-track) for the worst-case section on the whole line length is the most expensive solution and should be avoided.
2.1.5.3. Adoption to local situation
Depending on the sensitivity of the vicinity of the track way (adjacent buildings and their utilisation etc.) the application of vibration protection measures can be roughly recommended. The vibration reduction increases and the associated track building costs approximately rise correspondingly (from perhaps factor 1 to factor 4). The observation of these cost/benefit relations is therefore strongly recommended.
2.1.5.4. Combined measures for ballast tracks
A promising new development (test phase) is the stabilization of old or new ballast superstructures by polyurethane (PUR) in the load distribution area underneath sleepers. It compensates most of the disadvantages of normal ballast superstructures Furthermore, it reduces vibration and noise emissions. Exact measurement results are expected from an urban track application in Berlin.
For an application of polyurethane-stabilized ballast systems in tunnels, results of specific fire-tests are still needed. They should especially deal with temperature loads, fire-resistance and –distribution, release of toxic gases, generation of combustion products (smoke gases) etc.
2.1.5.5. Additional noise reducing measures on slab tracks
Compared to a ballast track bed with sleepers a slab track bed is associated with higher airborne noise emissions (up to + 5 dB(A)). If these lead to an exceeding of the limit emission values, further noise reducing measures need to be considered. Two possibilities can be recommended:
Absorbent plates as cover of the slab track way (reduction of noise emissions by some 2 to 3 dB(A));
Acoustic barriers (low walls with sound absorbing materials) running next to the track (attenuating effect up to 5 dB(A), depending on the situation).
Whilst the first solution is applicable both in tunnels an on bridges/viaducts, the second solution is more likely for bridges and viaducts, because there it affects the path of noise propagation most effectively.
2.1.5.6. Rail grinding important for noise reduction
The total noise emitted by wheels and rails is largely determined by the roughness of both running surfaces. Regular grinding of the rails is therefore of high importance for low noise (and vibration) emissions. Due to great weight the best grinding results are reached with rail-bound grinding machines, but they can only be deployed at night time so far, when no services are in operation (low running speed). A new focus is there for laid on “high-speed” grinding machines, which can nearly operate nearly at the same speed as the services. A continuous grinding during regular service is therefore possible, thus avoiding corrugation already in the developing stage and preserving a good condition of the rail surface.
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2.1.5.7. Curve-squeal mitigation
The most troublesome noise in urban rail transport is curve-squeal. It is very difficult to avoid, because it results from the stick-slip-effect of the wheel on the rail. Especially if the difference between the static and sliding friction values can be considerably reduced the typical tonal curve-noise is largely avoided.
The following measures have proved effective and applicable in tight curves of segregated tracks:
Lubrication of the wheel-rail-contact area (but observe necessary breaking characteristics of vehicles and avoid over-lubrication);
Damping the rail flange by specially designed rail dampers of elastic material (especially on existing tracks).
2.1.6. Recommendations for fire and rescue issues
2.1.6.1. Improved self rescue requirements
When tracks in tunnels and on bridges are due for renewal or refurbishment, fire and rescue issues are another key factor to observe. That means: The options for self-rescue and assisted rescue for all passengers (also for those with disabilities or reduced mobility = barrier-free-design) and for the crew should be improved to the greatest extent possible. This is a difficult demand and not to fulfil in all cases and at all circumstances. Especially in tunnels a solid and even (step-free) slab track design using fire- resistant (low fire-load) materials and easy-to-clean surfaces (= no combustible waste in track bed) is of high importance.
2.1.6.2. Horizontal exit/entry conditions
Track design in tunnels and on bridges should allow adjusted vehicle floor and platform heights at stops, to achieve nearly horizontal exit/entry and therewith optimal self-rescue conditions, when damaging event occur (e. g. fire, power outages, derailments, crashes). Such optimization has implications for track design and maintenance; in particular: regular checks and track refurbishment/renewal at earlier limit values of wear, to avoid unacceptable step heights and gap widths at the “interface” between vehicle and platform.
2.1.6.3. Avoidance of toxic gases
In tunnels, components of emergency walkways and crossings, wooden sleepers, elastic damping elements, switch cabinets, escape route signs, fasteners made from plastic or rubber, etc must not to any significant degree release toxic gases or generate combustion products with greater hazard potential than ordinary smoke gases in the event of fire.
Sheathing on cables must prevent fire from breaking out (short circuiting or overheating) and not generate any toxic substances. During renewal and refurbishment works, materials and equipment, which are not state-of-the-art in terms of safety risks, should be replaced.
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2.1.7. Recommendations for occupational safety and health considerations
2.1.7.1. Hazards and provisions
Works on a railway track (especially in the traffic area shared with other motor-vehicle traffic as sometimes on bridges) entail various hazards for the personal working within the track (e. g. from train operation, motor-vehicle traffic, construction site traffic as well as from the general running of the construction site). Therefore, special measures must be taken to protect the workers and to ensure, that rail operation is not jeopardised by large construction-site equipment.
For occupational safety and health measures, an EU harmonisation is currently sought in the form of minimum requirements. As a result, national accident-prevention measures are increasingly being replaced by EU regulations. These have to be observed and no national standards are allowed to fall below the EU minimum level.
2.1.7.2. General measures to minimise hazards
A thorough safety planning, consisting of organisational, technical and personal measures, is of vital importance. For most sites of renewal or refurbishments a combination of such measures leads to the best results.
Organisational measures consist of track closure, blocked runs or speed restrictions. Track closure should be avoided in public transport due to significant disruption of train operation. Blocked runs are not possible in public transport, because of short time intervals between passing train vehicles. Running at sight and with low speed when passing construction site is the preferred and recommended measure in public transport.
But observe: Organisational measures alone do not provide sufficient protection in most cases.
Technical safety measures include e. g. stop discs, barriers or light signals. In urban transport they can be recommended in connection with low speed train running operation at sight.
The most important personal safety measures on small (and short-time) railway construction sites (e. g. refurbishment works) are lookouts. They give an acoustic warning of approaching trains to those working within the track.
But observe: Acoustic (and visibility) tests under the worst possible conditions (loud background noise) should be conducted.
Where large-scale construction work is carried out (e. g. complete track renewal) a competent person for safety supervision should be appointed, who defines and coordinates the safety measures between the different parties.
As specific measures to reduce hazards from construction site traffic and the general running of the construction site can be recommended:
Safety-oriented site organisation (especially definition and marking of free safety areas and escape routes), safety training and a binding code of conduct for the employees as well as, observation (and supervision) of individual safety precautions.
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2.1.7.3. Specific safety measures on bridges with embedded or segregated tracks
Besides the general measures, work sites with embedded or segregated railway tracks in roads on bridges need additional technical safeguards against road traffic. A combination of e.g. lengthwise barriers, beacons, lights and marking is often practised and can be recommended.
2.1.7.4. Specific measures in tunnels and on viaducts
Track works in tunnels and on viaducts can largely be carried out without direct contact with the road traffic. But in contrast to track construction work at grade in streets some unusual features have to be taken into account here:
Restricted conditions for the execution of work; Restricted safety areas for the workers in case of danger; In tunnels: Supplying of sufficient fresh air and fire protection; Materials handling to the construction site must be executed lengthwise over the tracks etc.
Therefore the following safety precautions (additional to the general measures) have to be taken into account:
considering whether for safety and rescue reasons the tunnels should be designed as two single track tunnels with cross-connections at a distance between 300 m and 500 m instead of one double track tunnel.
defining and marking of specific safety areas and keeping them free from other users.
establishing a specific working group for safety (persons from owner, safety organisation and contractor), with focus on sagely precautions on the construction site.
definition of a detailed escape and rescue map for the construction site, coordinated with the local fire brigade and based on a hazard assessment.
monitoring the concentration of harmful substances (e.g. dust, quartz, smog) in the tunnel air and their reduction by an effective ventilation system.
2.1.7.5. Specific measures for driverless metros
If metro sections or lines are operated without drivers, measures must ensure that work in the track area can be performed just as safety as during conventional operation with a driver.
Such measures are:
signal dependent protection systems; conduction of work outside operating hours; taking automatic train control out of operation during the works and having a person or a system monitor the working section of the track.
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2.1.8. Tests on a test circuit and hydro-pulse-facility for embedded tracks
Public transport tracks embedded in road surfaces are subject to the following stresses and environmental conditions:
static and dynamic forces exerted by the rail vehicles; loads caused by heavy goods traffic (lorries, buses); changes in temperature, rain, brake sand, ballast chippings, frost.
These stresses very often cause damage at the interface between the embedded tracks and the road surface. Figure 2.1.1 shows typical damage in this area.
Figure 2.1.1: Damaged contact areas between road surface and embedded track
This situation entails not only substantial repair costs but also restrictions on public local rail transport and private motorised traffic while such track areas are reconditioned or renovated.
In practice, comparative studies of alternative forms of construction require years of observation, during which time it is very difficult to ensure a largely identical load. Realistic test bed studies achieve both a time-lapse effect and an equal load for all solutions being investigated.
The load on embedded tracks caused by passing lorry traffic was simulated at the STUVA test circuit. For this purpose test-bodies incorporating a similar rail-bed and fastening-system structure but different road surfaces were produced and installed in the test circuit. The structure of the test-bodies is described in detail in 2.1.8.2. The tests yielded conclusions on the following problems:
the durability of the superstructure at the rail-road surface interface; the influence of temperature; comparison of the different road surfaces in terms of the damage symptoms occurring.
Against this background also the test bodies used for the later on described tests belong to this three structure forms. All of them were realised in test-bodies. Additionally “green” track-bodies were also tested.
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2.1.8.1. Description of the test facilities
STUVA has a test circuit which can be used to investigate various problems with road surfaces. The facility consists of a circular roadway on which two lorry wheels roll connected by an axle. The entire axle load is transferred to the ‘roadway’ through the two wheels.
The axle is moved in the centre by a revolving turret. The latter is driven by an electric motor via a turntable thereby causing the wheel axle to rotate. The axle has two side pivots in the centre: these engage sliding blocks, which enable the axle to ‘rock’. The sliding blocks themselves can move vertically within the revolving turret such that the axle and wheels can be raised and lowered by means of two hydraulic cylinders.
The entire facility is located in a test hall, Figure 2.1.2, can be air-conditioned and is equipped with the necessary safety systems; the facility is operated via a control panel outside the test chamber.
Extra weight Revolving turret, drive Axle
Rubber-Wheels 16 Test bodies
Figure 2.1.2: STUVA test circuit machine with the 16 test-bodies of embedded rails
Test-circuit specifications: axle load Q = 10 t (= 100 kN; maximum with extra weight), spacing of wheel centres d = 10 m;
wheel load Fwheel = 5 t (= 50 kN), air-cushioned, no transmission of acceleration and braking forces, tyres: 445/65R22.5 (RHT 169K); electric drive to a wheel speed of V = 100 km/hr; temperature equalisation: -30°C to +60°C; maximum test-body height: h = 40 cm.
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2.1.8.2. Description of the test bodies embedded in road surfaces
In practice, embedded rails are subject to stress in different directions (transverse, longitudinal and diagonal). Figure 2.1.3 shows two examples.
Figure 2.1.3: Transverse and longitudinal stress on rails embedded in road surfaces.
These loads can cause damage to the contact area of rail and carriageway surface.
In order to conduct practical tests, the test-bodies had to meet certain conditions:
be representative of various types of carriageways; enable embedded rails to be driven over in the transverse and longitudinal direction; be a certain height, length and width (measurements predetermined by the test facility).
The test-circuit carriageway ring was subdivided to accommodate 16 test-bodies to study eight different types of carriageway, each with longitudinal and transverse embedded tracks.
Two test-bodies were sawn out of a track base plate (pre-cast concrete product with embedded rails) and thus delivered in the required dimensions. For the other test-bodies, 14 trapezoidal steel frames were made, which served as side formwork for both the concrete substructure and the differing structure of asphalt, paving and concrete. After the 14-cm high supporting slab was filled with concrete, the rails were installed in such a way as to reflect actual usage as far as possible and using the fasteners currently used in practice. All bodies share a continuous-elastic rail bed on the supporting concrete slab.
Figure 2.1.4 outlines the numbering of the various test-bodies.
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Testbody Type Supplier
1+2 Concretecovering GVB
3 + 4 Mastic asphalt Edilon)(Sedra
5 + 6 Concrete surface Hastra, Regum
7+8 Unboundedpaving Hastra,Regum
9+10 Boundedpaving Hastra,Regum
11+12 Asphaltsurface Hastra,Regum
13 + 14 Concrete with corkelast Edilon)(Sedra
15+16 Modulixsystem CDM
Figure 2.1.4: Overview of the arrangement of the 16 test-bodies in the test circuit
The production of the test-bodies does not correspond to the possibilities on the spot in every case. This applies particularly to all test-bodies which are condensed at the installation place (asphalt) or need a special underground (stones). The installation possibilities are limited by the soft steel sheet formwork of the test-bodies, too. This has to be taken into account at the assessment of the results.
The test-bodies were positioned appropriately using the test hall's ceiling crane and fastened by steel braces on a level concrete base course. They were arranged horizontally and vertically to achieve a largely level running surface (no height differences or gaps between the test-bodies) and thereby enable the facility to run quietly.
2.1.8.3. Conducting the tests on the test circuit
Before the tests were performed on the test circuit, the following had to be ascertained:
the test sequence for before/after comparisons; what measurement data should be recorded; how they were to be recorded and evaluated; the nature and scope of documentation; the time required.
The structure of the test-bodies and the course of the tests were coordinated with the participating transport companies from Karlsruhe and Bremen and the test-body suppliers. The test-bodies themselves were supplied free of charge by the track-construction companies.
In order to assess the resistance of the various combinations of track types, a minimum lifecycle of 10 years had to be simulated. An average daily load for heavy goods vehicles of 100 3-axle vehicles was assumed. Accordingly, over 10 years:
300 axles/day • 3,650 days = 1,095,000 wheel crossings.
The desired 1,000,000 or so wheel crossings were to be performed at a speed of 50 km/hr as customary in towns. The following results were obtained:
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A diameter of 10 m yields a path length of 31.4 m on the test ring. Where V = 50 km/hr (= 13.9 m/s), a time of t = 2.26 s is recorded for one rotation (= two wheel crossings). At 2.26 s x 500,000 rotations, the estimated theoretical run time of the test circuit is T = 1,130,000 s
( 313 hours). Based on 40 operating hours per week (= eight hours per day), the planned time required is approximately eight weeks. The total test duration, factoring in required facility-maintenance time, was approximately 10 weeks.
To ensure that the tests were based on as realistic a scenario as possible, air temperatures of -10°C, +10°C and +30°C were chosen so that the thermal loads on the test-bodies corresponded approximately to outside environmental conditions in Central Europe. The total required test time was divided into three cycles. In each cycle, the air temperature was altered in line with the predetermined criteria (Figure 2.1.5).
Cycle 1 Cycle 2 Cycle 3
pouring water 0 1 2 3
Measurement of the „pavement‘s“ surfaces Figure 2.1.5: Change in room temperature in the test hall during tests (circuit machine)
Prior to first use and after each cycle, the surfaces of the test-bodies were scanned with a laser to identify any possible changes in the rail bed and the rail/carriageway contact area.
The procedure below was followed during testing:
test-bodies installed in the test circuit; carriageway surfaces scanned in a longitudinal and transverse direction with a laser; test circuit: test cycle 1; carriageway surfaces scanned in a longitudinal and transverse direction with a laser; test circuit: test cycle 2; carriageway surfaces scanned in a longitudinal and transverse direction with a laser; test circuit: test cycle 3; carriageway surfaces scanned in a longitudinal and transverse direction with a laser.
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The main tests in the test circuit took place during the periods 21 February to 7 March, 2 April to 6 May, and 29 May to 11 June 2008. Testing had to be halted on the first occasion to enable replacement of two test-bodies which had failed to withstand the loads), while on the second occasion, maintenance was required on the test circuit. At various points, some test-bodies had to be subsequently stabilised to ensure that the facility remained stable. Overall, on average some 24,000 wheel crossings per day were achieved.
Each day, the test circuit was inspected prior to testing and all test-bodies examined and checked for visible damage. During the first few days, at -10°C and +10°C only slight surface abrasion and a small amount of displacement of the rail joint compound were observed. After the air temperature was set to +30°C during the first cycle more noticeable displacement of the rail joint compound was observed; at this temperature, the compound became very soft. During operation, the tyres reached temperatures of approximately 60°C and joint compound adhered to them; stuck to the tyres, the joint compound was thus distributed across all test-bodies. Test bodies 7 and 8 (bituminous-sealed paving stones on a layer of chippings) were particularly affected by displaced rail joint compound (Figure 2.1.6 left).
Figure 2.1.6: Displacements on test-bodies 7 and 8 at 30°C during the first cycle (left), Deep travel groove on the asphalt running surface (right)
As a result of this damage, test-bodies 7 and 8 had to be removed and replaced by ‘dummies’.
On the test-bodies incorporating an asphalt running surface, increasing indentation of the travel grooves was observed (Figure 2.1.6 right), whilst concrete surfaces and paving stones sealed with special mortar behaved in a very stable manner.
All elements are similar in that the rails did not move within the test body. Similarly, the damage to the compounds, regardless of its scale, occurred during the first test cycle in all elements, i.e. within a simulated life cycle of approximately three years.
During the third cycle, the surfaces were iced at -10°C. The temperature was briefly lowered to -15°C and the surfaces of the test-bodies were sprayed with water repeatedly to produce a layer of ice several millimetres thick. However, no noticeable effect was observed in any of the test-bodies when the load exerted by the wheels was applied again at -10°C following this brief stoppage.
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Test bodies 5 and 6 (concrete surface C30/37, concrete substructure) proved particularly stable. By contrast, test-bodies 7 and 8 (large granite cobblestones, unbound with bituminous joint compound, concrete substructure) were less resistant. The results indicate that granite pavement is only suitable for use in tracks often driven over by buses and lorries when combined with special mortar compound. In addition, concrete rather than asphalt should be used in areas of road/rail contact. Table 2.1.1 outlines further recommendations.
Carriageway structure Load by bus/lorry traffic
Test bodies Rail without low1) medium2) high3) Comments
1/2 Concrete Ri 59N X X X X
3/4 Mastic Asphalt Ri 59N X X X - Sensitive at high temperatures
5/6 Concrete, S49 X X X X
7/8 Paving, unbound Ri 59N X - - - Sensitive at high temperatures
9/10 Paving, bound Ri 59N X X X -
11/12 Asphalt Ri 59N X X - - Sensitive at high temperatures
13/14 Concrete solid Ri 59N X X X X bodies
15/16 Modulix system Ri 59N X X X X
1) < 10 passes per day ; 2) to 50 passes per day; 3) > 50 passes per day
Table 2.1.1: Recommendations for the use of embedded tracks with different pavements, different daily load due to vehicles (busses and lorries)
The measurements of the test-bodies (length, breadth, height) are determined by the dimension of the test circuit machine. To make the test bodies realistically, the at most possible measurements were chosen for this. An approach towards the actual solutions in the streets only an approximation is possible. This concerns particularly all embedded track types, which require a special compression or a special installation on the spot. For example all tracks are included with an asphalt surface or nature paving stones. Test bodies, which have to be produced from concrete, are almost unproblematic.
The number of test bodies to be examined with a series of experiments is limited on 16. Eight differently embedded tracks should be examined in the context of the project "URBAN TRACK". To be able to compare the results with each other, they had to be exposed to the same loads due to the wheels. This means that the rails had to be installed identically into the test bodies. They should be rolled over lengthways and crossways. On the spot the tracks are mainly run over in lengthways and crossways direction, too. This situation was simulated by the arrangement of the rails in the test bodies.
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Further influences how they exist in switches e.g. (spandrel in the common crossing) and by the installation of gauge tiebars on the spot could not be taken into account till now at the tests carried out. Special test bodies have to be made and subjected to a fatigue test at the circuit machine. This was not possible in the context of the ongoing project "URBAN TRACK".
The recommendations summarized in Table 2.1.1 can therefore only be transferred to such cases, which were simulated by the used test bodies. Cases of damage taken locally prove that the failure modes appeared at the tests show the reality largely. This covers the realism of the circuit machine for fatigue tests of tracks embedded in streets.
Summarizing it is to point out that only statements are permitted with respect to the boundary conditions available at the tests (construction of the test bodies, load due to the rubber tyre, temperatures etc.). The recommendations contained in Table 2.1.1 have to be understood only on this background. At present, a generalization on all possible other application cases is not possible.
If more detailed statements are required, e.g. influence of gauge tiebars or switches, corresponding test bodies have to be made and subjected to fatigue tests at the circuit machine.
2.1.8.4. Conclusion
To determine the influence of the load on tracks embedded in road surfaces exerted by heavy goods traffic (buses and lorries), eight different carriageway and track structures were tested on a test circuit. Corresponding test-bodies were produced for this purpose. These were then ‘driven over’ at a speed of V
= 50 km/hr and axle load of Faxle = 100 kN.
The key carriageway types studied were: asphalt (in two variants); pavement (in three variants); concrete (in three variants).
The test-bodies were rolled over in three temperature cycles at temperatures of -10°C, +10°C and +30°C room temperature. Each cycle comprised approximately 330,000 wheel crossings (a total of approximately 1 million wheel crossings). This simulated a real load of over 10 years.
Other than the pavement structure with elastic joint sealing compound, all other test-bodies withstood the load.
The measurements of the static vertical and horizontal stiffnesses found clear differences between individual test-bodies. Subsequent checks in this respect revealed hardly any differences.
The surfaces of the individual test-bodies were ‘deformed’ in various ways by the wheel crossings. Most significantly affected was the unbound pavement, followed by the asphalt base courses. By contrast, after the tests the concrete bodies remained largely unaffected.
In summary, the tests found that all test-bodies with a concrete structure up to the surface (which also includes a natural-pavement structure with concrete backfilling) withstood the tests well. This structure is to be recommended for heavy loads (buses and lorries).
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The green tracks studied and which must be suitable to allow emergency-vehicle access, yielded different results. These tests were performed with a lower axle load, at slower speed and for a shorter test duration
(V = 30 km/hr and axle load of Faxle = 70 kN).
The solutions incorporating artificial grass on a solid concrete body withstood the loads without sustaining any significant damage. By contrast, during the first part of the test the test-bodies designed for planting with sedum failed when subjected to a load for only a short period. The two test-bodies with a strip of drainage concrete approximately 10 cm wide alongside the rail withstood the loads for the longest period but ultimately these, too, failed. After swapping the drainage layer material for drainable base layer material in two test bodies (drain concrete version), and compression of the layer these two test bodies withstood the remaining test (4,600 wheel crossings) without any damage.
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2.2. OPTIMAL MAINTENANCE METHODOLOGY (WP2.2)
The work package WP2.2, on optimal maintenance methodology, is made of three work packages:
Visual inspection & maintenance (Proposal for a harmonised inspection and maintenance standard): WP2.2.1, developed by FCP.
Predictive and preventive maintenance of metro tracks: WP2.2.2, developed by INSA, INRETS and D2S.
Preventive maintenance of embedded tram tracks (Rail wear in curves and special track work for trams): WP2.2.3.
2.2.1. Visual inspection & maintenance (WP2.2.1, developed by FCP)
2.2.1.1. Introduction
The objective of the work package “Visual inspection & maintenance” was to create a comprehensive preliminary draft specification for urban railway tracks of public transport such as tram and metro. The draft specification was created with an emphasis on visual inspection and is applicable for all urban traffic network operators. The specification was aimed in particular at the small and medium size urban traffic network operators.
2.2.1.2. Strategy used and description of the methods
The draft specification was created using a step by step methodology. External experts from universities and operators assisted in compiling a preliminary draft specification. This draft specification formed the basis for the discussions with the operators and the consensus finding process. The proposal document and a questionnaire were distributed to several operators Urban Track members and other experts to ascertain their views and opinions. Unfortunately the number of responses collected was very limited and therefore the strategy was altered. Subsequently it was decided to identify and contact relevant European operators and experts in the fields of inspection and maintenance to submit to them the draft specification. In addition, independent personal meetings were organised which provided a forum were relevant information, comments and remarks were collated through personal discussion.
2.2.1.3. Results
The final step of the intended consensus finding process was a short survey with three questions:
if the expert comments represent the official position of the represented operator, if the operator is interested in a European standard for inspection and maintenance and if the operator would support the standardisation work.
Results collected in interviews with relevant European operators are submitted in the Table 2.2.1 below.
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Standard would of value for the company; Operator's Opinion/remarks are interest in existing the EU Interest in the Metro Town Operator address Date of visit Proposal of the Standard visual inspection & maintenance representing for the Standard denoted as: absolute future support of Tram companies opinion ("in fever"), interested, work on Standard perhaps, not interested, strong opposite
They are interested to participate in the "Wiener Linien" supported the creation of the proposal. The comprehensive Viennese Metro and future tramway in-house standard was provided as helpful background. Nevertheless the staff of “Wiener The interest in defining the Wiener Linien GmbH & Co KG standardisation Linien “ is of opinion that one-sided definition of limit values for urban track inspection and Technical expertise of the integral Standard for urban 1 Vienna Erdbergstraße 202, A- 1030 M+T several process and give maintenance is not currently purposeful because of the current rapid change of European knowledge expert tracks is not conceived at the Wien their contribution in base in defining the rules and standards.The present research has shown that one-sided limit values moment. domain of creating could be meaningful only if they would be given for particular track in particular urban conditions. mechanisms and criteria for the future GVB Grazer Verkehrsbetriebe Grazer Stadtwerke AG The operating staff in Graz is not be willing to deal with Standards in English language. Therefore no Not interested because the Verkehrsbetriebe, Technische 2 Graz T 26.03.2008 direct remarks about the proposal are available. Nevertheless the wear limits of the tramway in Graz State of the company operator is not able to deal with Services FAHRWEG, have been provided and will be taken into accout. the document in English Steyrergasse 116/II/Zi.208, A- 8010 Graz, Austria DVB Dresdner If a long experience in business Verkehrsbetriebe AG, is available, standard must Dresden advised that the recommendations in the standard proposal are useful for operators with wide 3 Dresden Hohenthalplatz 7, 01067 T 04.06.2008 Yes reflect this and should not open experience of maintenance. For new operators, these recommandations should be taken with caution. Dresden, Postfach 100955, inconsistent to the experience; 01079 Dresden then acceptable If a long experience in business is available, standard must VBK Verkehrsbetriebe 4 Karlsruhe T 30.03.2008Involvedintheconsensusfindingprocess Yes reflect this and should not open Karlsruhe inconsistent to the experience; then acceptable
If a long experience in business is available, standard must bsag Brehmer Straßenbahn 5 Bremen T 05.06.2008Involvedintheconsensusfindingprocess Yes reflect this and should not open AG inconsistent to the experience; then acceptable STIB Sociétédes Transports Intercommunaux Operator is of opinion that the proposal is a good guideline for urban railways. It comprises: many de Bruxelles aspects such as: geometry, construction, inspection, preventive and corrective maintenance as well as Opinion of the technical 6 Brussels M+T Interested Yes Avenue de la Toison d'Or, 15 measures that should be implemented in inspection&maintenance policy. They support work in expert of the company 1050 Brussels creating the EU Standard. RueRATP de Stassart, Régie autonome 36 des transports Parisiens Proposed standards are not Département EST - Unité I2E- convenient to metro conditions in PTEC/VOIE The proposal of the Standard is not quite convenient to Paris track conditions. For example some Paris, therefore there is no high 7 Paris LAC VE01 M+T 12.03.2008 metro lines are running on rubber tyres. Therefore RATP prefers using the EN 13484 modified to the State of the company Perhaps interest in implementation and 56, rue Roger Salengro metro conditions of Paris. participation in standardisation 94724 Fontenay-sous-Bois process. Cedex
Compagnie des Transports 8 Strasbourg T Theremarkshavenotbeensentuntilnow. Interested open Strasbourgeois - CTS
Interested but since they already Porto operator analyised the proposal in detail and gave remarks refered to intervention and alert limits established many supporting Metro do Porto, SA Avenida Technical expertise of 15/16.09.200 and enclosed the table with current implemented tolerances in Porto metro company. It should be documents and the standard 9 Porto FerànoMagalhàes, 1862, 7° M+T experts' team for metro Yes, occasionally 8 specified to which speed is the proposal based on, tolerances should be given for concrete and ballast does not fit fully to a major part 4350.158 Porto, Portugal maintenance&inspection track separately. Some terminology in the proposal has to be more clarified. of the network, it would be not of a great value for the company
A few remarks about the Standard were given: There was the wish for new geometric measurement TMB Transport metropolitans methods and devices for the inspection of levelling and horizontal alignment. The absolute coordinates deBarcelona Av.Del 10 Barcelona M+T 09.06.2008 of the track are not such important and mostly unknown. Therefore it is senseless to compare existing State of the company Interested Yes Metro s/n 08902 L'Hospitalet and projected coordinates. Relative measurements should be prefered in urban tracks with correlation de Llobregat of lateral and vertical derivations (limits).
Metro de Madrid There was no proposal available at the time of Madrid visit but the document was sent afterwards. The Dr. Esquerdo, 138. 28007 11 Madrid M(+T) 15.02.2007 operator is of opninion that the Standard icould be of a great value for the company and therefore is Technicalexpertise Absolute Yes Madrid interested to be involved in the further work on Standard. Cavanilles, 58. 28007 Madrid Centro Midland Metro Birmingham 28.04.2008 Technical remarks were given. Some terminology has to be clarified. A hardcopy of the proposed 12 Birningham M+? State of the company Interested Yes Centro House, 16 Summer Cologne standard with the remarks drawn in was delivered. Lane, Birningham, B19 3SD
Andy Steel is the technical 13 London London Trams M+T 27.01.2009 Questionnaire handed over personlly in January 09 Interested Yes resp. Engineer
The operator agreed with the content of the Standard proposal. The special intention should be paid to Perhaps. At the moment their Metronapoli Yes, especially if 05/06.05.200 implementtaion of lubricant method according to opinion of metro staff in Naples. The second interest is focused on the 14 Naples Via Ponte dei Francesi, 37/d - M+T State of the company they would be 8 important issue is ultrasonic inspection for welded rail joints as a measure for reducing the risk of rail standard impact on maintenance 80146 Napoli involved in site tests cracks and fractures. cost reduction
Tom Potter is the technical 15 Bergen bybanen,NSBlokaltog T 28.04.2008 The remarkshavenotbeensentuntilnow.(inspiteofseveralreminders) Interested Yes resp. Engineer
Yes, technical responsible 16 Helsinki YTV M+T 26.01.2009 The remarks have not been sent until now. staff will be involved in the Open Open answers
BKV Budapesti Transport A lot of information about weakness of the old track system, it's improvement and renewal as well as 17 Budapest 1146 Budapest, Hungária T 17.04.2008 the advantages of the new one have been presented in detail. The table with limits values krt.46 implemented in maintenance and inspection policy in Budapest transport company is given.
The main part of tram lines in Warsaw is track with segregated right of way. According to problem Tramwaje Warszawskie generated by noise and vibration, since 2000 the new strategy and method are in implementation in Technical expertise of 18 Warsaw 01-424 Warzawa, al. Prymasa T 16.05.2008 operating the rail system. To reduce the noise effects an anchored system adopted from Germany is experts team for tram track Absolute Yes Tysiaclecia 102, Poland used. In spite the efforts of operator staff in Warsaw remarks about the Proposal have not been maintenance submited.
"Not interested" at the moment, Existence of the but being aware of importance of integral EU Standard DPP Dopravní podnik hl. M. 28.04.2008 There are some remarks about measurements of horizontal alignment. The Czech operators (refer to standardisation process. could be useful in the Prahy, akciová spolecnost, Cologne 19 Prague M+T Brno operator too) are not involved in the creation of national standards. They want to avoid tougher State of the company Implementation of future Sokolovská 217/42, 190 22 12.06.2008 regulations of their ministry due to new European standards. maintenance&inspection policy maintennace&inspec Praha 9 Praha in the future should be based on tion policy of the integral EU Standard European countries
The operator in Brno uses the national standards for tram operating system. Therefore their They are interested The operator generally support collaboration in project was done in domain of information about track system types as well as in to participate in the Dopravní podnik města Brna, Opinion of the technical the cretion of the Proposal. It 20 Brno T 13.05.2008 inspection and maintenance policy carried out within the company. However the Brno operator is ready future a. s expert of the company could be of value for the and interested to collaborate in standardisation of maintenance and inspection policy for European standardisation operators' companies track systems. process.
intergrated in the project intergrated in the network of operator not intergrated but intrerest Table 2.2.1: Operator Interviews
An example of the effect of the use of the standard on life cycle costs (LCC) is given in the report. It describes the approach of the LCC-calculation for the SP 2.2.1 “Visual inspection and maintenance”.
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This case compares two maintenance variants based on the maintenance categories defined in the “Proposal of European Standard for Track Inspection and Maintenance”. Table 2.2.2 shows the different maintenance measures which are assigned to the categories.
Element Failure / Reason Measure How often / indication Classification *) rail curve of small radius lubrication - fixed continuous comfort/ station environment wheel squeal lubrication - fixed continuous comfort/ station environment corrugated rail, burr grinding, deburring of after visual cost-effectiveness formation rail and rail joint inspection; exceeding limits for track gauge rail breakage applying joint bars; after visual safety speed reduction or inspection; service break if feedback from necessary until rail driver breakage can be repaired track gauge gauge narrowing grinding, deburring of reaching safety safety rail and rail joint limit reaching cost-effectiveness intervention limit reaching alert comfort/ limit environment gauge widening build-up welding or reaching safety safety replacing rail limit reaching cost-effectiveness intervention limit reaching alert comfort/ limit environment
turnout preventive mobile lubrication after cleaning cost-effectiveness maintenance preventive cleaning and before and after cost-effectiveness maintenance lubrication of point winter mechanism
turnout & corrugated rail, burr grinding, deburring of after visual cost-effectiveness crossing formation rail inspection; feedback from driver
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Element Failure / Reason Measure How often / indication Classification *) sufficient resistance to tamping after visual cost-effectiveness ballast bed longitudinal and inspection lateral creep is not guaranteed contamination screening of ballast after visual cost-effectiveness inspection and/or feedback from driver
sleepers breakage replace after visual safety inspection
drainage failure cleaning, renewal in case of failure safety
planting mowing, weed-killing after visual cost-effectiveness vegetation on inspection the tracks pavement - ► cracks -single or removal and relaying after visual cost-effectiveness asphalt netlike inspection ► nicks and joints ► depressions and bulges ► lane grooves ► asset erosion ► lack of adhesion pavement - ► tilted or removal and relaying after visual cost-effectiveness paving protruding paving or replacement by inspection stones asphalt ► depressions pavement – ► tilting slabs removal and relaying after visual cost-effectiveness concrete slabs ► sink, shift or brake or temporary inspection of slabs replacement by asphalt ► loose slabs because of defect bedding ► protruding steel edges Table 2.2.2: Review of the different maintenance measures
2.2.1.4. Conclusions
The information gathered from operators varied greatly from only general statements to very detailed comments. Discussions were sometimes difficult as the operator personnel undertaking the inspection and maintenance work typically was not accustomed to working with English language documents.
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Through the course of these discussions further aspects have been identified that have made the definition of a uniform standard for track inspection and maintenance very difficult:
Confidentiality of “in-house procedures” for inspection and maintenance,
urban operators, which often belong to the local community are conscious of safeguarding regional jobs and are reluctant to support the global companies,
for global working component suppliers the market is small, diverse, competitive and not significant,
apprehensiveness of operators towards European harmonisation and standardisation,
for large operators, with vast in-house expertise and sophisticated regulations and procedures concerning the track – rolling stock interaction, a harmonised standard would be either irrelevant or a step backwards.
The result of the survey to the operators showed only moderate interest to the standardisation and rather opposition within significant operators.
In conclusion the working process for the proposal of the standard showed the diversity of urban track systems, maintenance strategies, legal form of the company, opinions of operators and their preferences. A standardisation is not recommended, however the document could be helpful as voluntary guidelines for operators creating their own “in-house procedure”.
2.2.1.5. Bibliography
[1] Girnau G., Krüger F. (2007), Local and regional railway tracks in Germany, Verband Deutscher Verkehrsunternehmen (VDV) (Hrsg.), Alba Fachverlag, Düsseldorf
[2] EN 13848-1 Railway applications/Track – Track geometry quality, Part 1: Characterisation of track geometry
[3] Wu H., Shu X., Wilson N. (2005), “Flange Climb Derailment Criteria and Wheel/Rail Profile Management and Maintenance Guidelines for Transit Operations, TCRP Report 71 (Volume 5), Washington, D.C.
[4] Grassie Stuart L. (1995), Measurement of railhead longitudinal profiles: a comparison of different techniques, Wear 191, p. 245-251, Elsevier Science S.A.
[5] TCRP Report 71, Flange Climb Derailment Criteria and Wheel/Rail Profile Management and Maintenance Guidelines for Transit Operations (USA)
[6] Naue M. (2003), Messmethoden zur Bestimmung von Verschleiss und Lagegenauigkeit von Straßenbahnschienen, Diplomarbeit, Universität Fridericana Karlsruhe, Institut für Straßen- und Eisenbahnwesen, Karlsruhe
[7] http://railmeasurement.com/cat.htm
[8] Grassie Stuart L., Edwards J., Shepherd J. (2007), Roaring Rails – an enigma largely explained, International Railway Journal, July 2007, p. 31-33
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[9] EN 13848-5 Railway applications/Track – Track geometry quality, Part 5: Geometric quality assessment
[10] APTA RT-S-FS-002-02, Standard for Rail Transit Track Inspection and Maintenance, Authorized September 22, 2002
[11] EN 13674-1 Bahnanwendungen - Oberbau - Schienen - Teil 1: Vignolschienen ab 46 kg/m
2.2.2. Predictive and preventive maintenance of metro tracks (WP2.2.2, developed by INSA, INRETS and D2S)
This chapter deals with “predictive and preventive maintenance of metro tracks”. Its objectives are to develop optimized inspection methods and maintenance procedures guided by a low cost efficient monitoring system and taking into account LCC aspects.
At the beginning of the project, during a meeting in London (SP2 meeting, 11/2006), it was decided to split the topic in several parts:
first a more theoretical study (WP2.2.2a), especially of interest to the larger metro networks, developed both by INSA for a better understanding of rail lubrication impact, and by INRETS to solve the problem of rail track reliability estimation, and second a direct application study, the Manila case (WP2.2.2b), providing low cost solutions in a short term, especially of interest to the smaller metro and LRT networks.
2.2.2.1. Understanding rail lubrication impact (WP2.2.2a, developed by INSA)
This part of the study is very specific: INSA work as part of WP2.2.2.a was to investigate rail lubrication in the aim of optimizing the frequency of maintenance operations while minimizing friction and wear as a function of the contact’s geometry, contact conditions, mixture rheology. The term mixture will be commonly used in INSA work. The mixture is composed of a mixing of detached metallic particles (from wheels and rail), mineral particles (sand) and lubrication oil.
Detached particles Lubrication:"initial" [oil + asphalt]
Mixture (3rd body)
Contact geometry
Figure 2.2.1 Mixture between rail and wheel Wear flow
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It is the first time that the mixture present at the interface between the wheel and the rail has been taken into account and its rheology been characterised, on the basis of the analysis of a RATP example. The tribological approach developed for the RATP network could be transposed to others networks involved in the project.
The rheology tests were performed on a Bridgman simulator (used in this case as a “rheometer”). Observations of the anvils surfaces were performed after tests with optical microscope. They highlighted, whether the mixture is dried or not:
oil bleeding from the mixture and the trapping of the additives of oil in the roughness of the anvil; “selective” ejection of parts of the mixture out of the contact surface.
The additives trapping highlights chemical reaction of additives with surfaces anvils. The torque has been registered during the tests and highlights that probably the oil-bleeding modifies the limit conditions – friction coefficient - of the contact. The amount of the ejected mixture or parts of the mixture out of the contact is higher in the case of the fatty initial mixture compared to the dried one. This can be due to a different initial amount which is difficult to control.
The chemical reactions of the oil and/or asphalt and/or additives of oil with fresh surfaces of the detached particles – highly reactive – can also effect on the oil bleeding and the ejection of mixture.
Conclusions A good lubrication process reduces the wear and the friction in the wheel flange and flange root, meanwhile keeps the rail head dry for optimal adhesion (traction and breaking). Whereas in urban rail networks, wheel rail lubrication in narrow curves is an important topic in terms of maintenance cost, life time and security very few research investigations have been done on this complex problem. As a consequence this work performed by INSA on rail lubrication was exploratory.
The research has been divided in four main parts:
First INSA meets lubrication experts for the wheel-rail contact to understand how the process adjustment and the maintenance are done on RATP network1 (the tribological approach developed from RATP network study could be transposed to others networks).
Secondly the tribological properties of the mixture are characterised. To do this, sampling is done on RATP network.
Thirdly the test benches used are described, and then the formation and the tribological behaviour of the “wear” mixture (initial lubricant + wear particles) investigated.
Fourthly a numerical model will be settled to access to local wheel-rail contact characteristics (i.e. contact geometry evolution during traffic, contact positions on the rail surface, contact pressures,
1 RATP network has been chosen at the beginning of the project for a first investigation, especially to reduce travel costs.
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plastic deformation… ) under various lateral loading conditions from straight track to sharp curved track.
Setting on an on-site experimental feedback, RATP has found for one initial lubricant the way to form in situ an efficient mixture. Best practice has defined a “good lubrication” state, and the maintenance policy in term of lubrication is to maintain this state of lubrication. From our own experience, previous work highlighted the same state on others networks (SNCF for example), that’s why this “good lubrication state” was chosen as reference case. It is now obvious that a good lubrication required the formation in situ of a mixture. This mixture is the melting of the initial lubricant and the particles detached from the wheels and rails. Thus the study focused on the tribological study of the mixture.
The chemical composition and the texture of this mixture have been investigated with different specific tools: Photonic Microscope, Environmental Scanning Electronic Microscopy (SEM) and X-ray energy dispersive analysis (EDX).
The mixture rheology has been studied on a Bridgman simulator which allows reproducing contact pressure and high shearing conditions. Different mixtures sampled on site have been tested and their functioning analysed (range of friction coefficient from 0.005 to 0.015, localisation of the velocity accommodation in the skin (interface) or in the bulk of the mixture).
A roller / plane simulator of INSA was modified in link to the wheel flange-rail active root flange contact configuration. Then tests have been performed in the aim:
to investigate and to begin to understand the formation of the mixture and its tribological functioning. Special attention was given to its life time (maintenance) and the friction coefficient value (security, derailment and wear),
to get a representative and useful tribological tool, enabling to validate new lubricants and new rail profiles under realistic contact conditions.
As the reality is complex, it is necessary to draw a parallel between the results of the laboratory tests and the results obtained by expertises of samples issued from real site. This approach allows validating the laboratory results.
From the experimental investigations, a tribological scenario of the functioning of the mixture leading to a low friction coefficient (efficient mixture, 0.05<µ<0.01) can be proposed (figure 2.2.2). Once this mixture is formed, its rheology allows to fill in the local roughness of the rail (from µm to tenth of µm) and thus a smooth surface is created ; this last allows the velocity accommodation to be activated in a very thin superficial layer (nm) composed by the initial lubricant additives adsorbed on this smooth surface (surface complex). The initial lubricant is itself brought on this surface by bleeding caused by the high contact pressure (and perhaps by shearing). The different values of friction between mixtures can be explained by the localization of the velocity accommodation: in the extreme surface of the mixture (skin) or in the bulk of the mixture.
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Figure 2.2.2: A tribological scenario
The control of the lubrication process requires the control of the initial formation of an efficient mixture and its holding in the contact, which means a specific optimized rheology of the mixture, a localization of the velocity accommodation (surface) with a low friction. Its formation can be in situ or ex situ. Given the state of current knowledge, it does not appear possible to formulate a product (ex situ) whose rheology is similar to that of the mixture and which can be deposited on the active flange of the rail surface. Consequently, it is necessary to orient efforts towards the use of controlled rail-wheel wear to obtain the “right” mixture. Its formation has to be in situ. Thus the two phenomena, leading to the formation of this efficient mixture, have to be investigated:
the detachment of particles, the physico-chemical reactivity of the particles with the initial lubricant (oil + additives) under tribological stresses (pressure, shear).
The mechanisms of the lubrication of the active rail gauge involve complex coupling phenomena, which do not allow elementary parametric studies on site (in practice, the parameters involved are never modified one by one). As for a consequence, a laboratory test developed in this study will allow to finish the understanding and then to investigate new biodegradable (for example) lubricants. Note that the validation of a new lubricant is in progress. This new tribological tool enables to preset new lubricants under realistic contact conditions in laboratory, before to perform qualifying tests on industrial test bench or on site.
The numerical modeling proposed in parallel of the experimental simulations allows investigating the local effects of the local friction and of the contact geometry (i.e. new, worn…) on the local stresses fields and thus on the detachment of particles. Last, but not least, further work should integrate:
the “right” behavior laws of the materials under stresses as those found under contact, i.e. high hydrostatic pressure and high shear gradients,
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the mixture, which could be taken into account thanks discrete elements modeling
Despite its high prospective level, this study brings experimental and numerical tools:
to finish the understanding of the lubricating mechanisms involved in the contact in curves, and thus of the tribological functioning of the mixtures, to specify more precisely criteria for quantification of the rail lubrication in the aim to control the maintenance, to formulate some new lubricants, to understand the geometric effects of the wheel and the rail.
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Active flange lubrication
A Reality Simulations N
60 mm Experimental Numerical A
“Patine“ Mixture L Contact location (specific surface aspect, i.e. the good 3rd body to lubricate)
Y CPress (MPa) 7 trains, Extreme pressure oil 750 S RATP lub. cond. µ<0.02 µ<0.1 20 50 E
S Flows of the mixture Geometry effect
Effect of µ Smooth surface Qualitative 1 mm validation Location Pressure
S Effects of the oil additives p
e Semi quantitative
c validation
i Representative Conditions of the Effect of the f test mixture formation profiles i c Life duration of the mixture a t i o
n Lubrication Additives Profiles conditions
Others networks Validation
Specification
Figure 2.2.3: Scenario of mechanical-chemical operation of the mixture
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2.2.2.2. Solving the problem of rail track reliability estimation (WP2.2.2a, developed by INRETS)
This part of the study is dealing with mathematical modelling as a support tool to help solving the problem of rail track reliability estimation. Nowadays, reliability analysis has become an integral part of system design and operating. This is especially true for systems performing critical applications. Typically, the results of such analysis are given as inputs to a decision support tool in order to optimise the maintenance operations. Unfortunately, in most of cases, the system state cannot be evaluated exactly. Indeed, it is uncommon to be able to deterministically describe the process each component, part of a complex system, reaches a failure state. This is one of the reasons which have led to the important development of probabilistic methods in reliability.
The aim of this sub-project is to develop a virtual maintenance tool that is able to model and integrate the track degradations in relation to inspection and maintenance rules. This tool, called “Graphical Duration Model”, DGM, - see below - will be implemented in order to take into account the random behaviour of degradation processes. Partners RATP and INRETS have experience with these methods. This kind of mathematical tool can unwind the life cycle of a specific component and carry out its interaction with the maintenance operations in accordance with a given strategy. So, optimised maintenance rules can be highlighted for given exploitation conditions. One can thus quantitatively evaluate predictive or opportunist maintenance strategies versus curative ones, in terms of financial costs as well as safety or availability costs.
This chapter presents the results obtained during the first year of the project. First, the theoretical frame of the study (PGMs and DPGMs theory and some details about the parameters learning) is introduced. Then is explained how to model the reliability of complex systems using a proposed graphical approach. Finally, some conclusions and perspectives are discussed.
BACKGROUND A wide range of works about reliability analysis is available in the literature. For instance in numerous applications, the aim is to model a multi-states system and therefore to capture how the system state changes over time. This problematic can be partially solved using dynamic modelling (i.e. Markov framework) [1]. The major drawback of this approach comes from the constraint on state sojourn times which are necessarily exponentially distributed. This issue can be overcome by the use of semi-Markov models [14] which allow considering any kind of sojourn time distributions. On the other hand, one can be interested in modelling the context impacting on the system degradation [11]. A classic manner to address such an issue consists in using a Cox model [6] or a more general proportional hazard model [12]. Nevertheless, as far as we know, it is unusual to find works considering both approaches at the same time.
Moreover, recent works in reliability involving the use of Probabilistic Graphical Models (PGMs), also known as Bayesian Networks (BNs), have been proved relevant. For instance in [4], the authors show how to model a complex system dependability by mean of PGMs. [13] explains how fault trees can be represented by PGMs. Finally in [19], authors show how convenient Dynamic Graphical Models are in order to study the reliability of a dynamic system represented by a Markov chain. Our work aims to describe a general methodology to model the stochastic degradation process of a system, allowing any
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kinds of state sojourn distributions along with an accurate context description. We achieve to meet these objectives using a specific Dynamic Probabilistic Graphical Model (DPGM) called Graphical Duration Model (DGM).
PROBABILISTICS GRAPHICAL MODELS
Definitions Probabilistic Graphical Models (PGMs), also known as Bayesian Networks (BNs) [10], are mathematical tools relying on the probability theory and the graph theory. They allow to qualitatively and quantitatively representing uncertain knowledge. Basically, PGMs are used to describe in a compact way the joint distribution of a set of random variablesXX1,..., N . Formally, a PGM, denoted by M, is defined N as a pair G, p , where: ii1
G=(X, E) is a Directed Acyclic Graph (DAG). XXX 1,..., N is a set of nodes representing random variables and E is a set of edges encoding the conditional independence relationship between the variables in the model. Thus, G is a qualitative description of M.
N p i i1 is a set of Conditional Probability Distribution Functions (CPDs) aiming to describe the
quantitative aspect of the model. It is worth noting that if the random variable Xi takes its values in a 1 K finite and countable set Xi (e.g. Xi x i,..., x i ), the CPD of Xi can be defined by a Conditional
Probability Table (CPT). On the other hand, if Xi is an infinite set then pi is a conditional density function.
The underlying conditional independence assumptions introduced by this modelling allows to economically rewriting the joint probability distribution:
th where i denotes the subscripts of the i variable parents in the graph. Thereby, it is important to remark that X is no longer a single random variable but a set of random variables containing the parents of Xi i in the graph G.
CPD parameters learning Both the qualitative and quantitative parts of a PGM can be automatically learnt [17] if some data or experts’ opinions are available. The latter problem can be boiled down to probability distribution N estimation. We consider that the CPDs of the model are the p where θi represents the parameters of i i1 N th the i CPD. Thereby, the objective becomes to deduce estimates of i i1 using the available knowledge. A classic manner to tackle this problem is to use the Maximum Likelihood (ML) method to exploit
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information in databases. If some a priori information is also available (e.g. experts knowledge), one can use bayesian methods [8] and compute Maximum A Posteriori (MAP) estimates of the parameters. To that end, it is possible to use the factorisation property of PGMs, so that each θi can be locally estimated using only the ith CPD.
M Suppose that we have a database containing M observations of each variables Xi, denoted by x , i, mm1 then the ML estimate of the ith CPD is compute by solving the following equation:
If some a priori knowledge is available about i, equation (3) becomes:
where is a function aiming to model the knowledge available on the parameter.
Inference in PGMs Using PGMs is also particularly interesting because of the possibility to propagate knowledge through the network. Various inference algorithms can be used to compute marginal probabilities when the model becomes more complex. Inference in PGMs [9] allows taking into account any variable observations (also called evidence) so as to update the marginal distribution of the other variables. Without any evidence, the computation is based on a priori distributions. When evidence is given, this knowledge is integrated into the network and all the marginal distributions are updated accordingly.
Finally, it is important to notice that such a modelling is unable to model the dynamic of a non stationary system. For instance, in reliability analysis, one can be interested in modelling how a system changes from an "up" state to a "down" state over time. For this kind of problem a possible solution consists in using the dynamic extension of PGMs which are presented in the next section.
DYNAMIC PROBABILISTIC GRAPHICAL MODELS Dynamic Probabilistic Graphical Models (DPGMs), also known as Dynamic Bayesian Networks (DBNs) are convenient tools to represent complex dynamic systems. The term "dynamic system" makes reference to a system of which state can change over time but with a fixed structure. To that end, DPGMs allow variables to have temporal (or sequential) dependencies.
Strictly speaking, a DPGM is a way to extend PGM to model probability distributions over a collection of random variables XX,..., . A DPGM MD is defined [16] to be a pair MM, where: 1,t N , t t * 1
M1 is a PGM which defines the prior distribution PXX 1,1,..., N ,1 as in equation (1).
M is a s-slices Sequential Probabilistic Graphical Model (s-SPGM), also named s-slices Temporal Bayes Net (s-TBN) in the literature. s makes reference to the temporal dependence order of the model.
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In this paper, we will limit ourselves to the case of a 2-SPGM which mean that the present (slice t) is only dependent on the one step past (slice t-1). It is worth noting that we would rather use the more generic term "sequential" instead of "temporal". Indeed, in many applications (e.g. genetic or reliability), the dynamic of the studied system does not necessarily rely on time (e.g. genetic sequence, number of mechanical solicitations for device).
Basically, M is also a PGM used to define the transition model which describes the dependencies between variables in slice t-1 and variables in slice t. It aims to specify the CPD
PXXXX 1,t,..., N , t 1, t 1 ,..., N , t 1 taking advantages of the factorization property in PGMs:
where X is a set of the parents of X which could contain variables in the slices t and t-1. i ,t i, t
Note that the slice of M is identical to M1, the latter can be omitted and the DPGM is strictly equivalent to a 2-SPGM.
T Then, it is possible to deduce the distribution PXX,..., by "unrolling" the 2-SPGM until we 1,t N , t t1 have a sequence of length T:
The fact that t is an integer means we only consider discrete stochastic processes. This restriction is not very penalizing in survival analysis because the duration variable is often expressed as an integer (e.g. number of hours, days, years, solicitations… before a failure).
The figure 2.2.4 shows how to represent a classic Markov chain subjected to two covariates with a DPGM.
This kind of simple model can be use in reliability to model the state of a system, Xt, given some contextual variables, Z1 and Z2, over time.
Figure 2.2.4: A Markov chain with covariates represented by a DPGM.
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Finally, as it is possible to consider a DPGM as a big unrolled PGM, it is clear DPGM inherits the convenient properties of classic PGM. Indeed, learning methods do not change when using DPGM. Concerning the inference problem, most of the methods are based on static PGM inference algorithms [16].
INTRODUCTION OF THE GRAPHICAL DURATION MODELS Recent works in reliability involving the use of PGMs have been proved relevant since they are particularly suitable to model the dynamic of a complex system [4]. Nevertheless in the field of reliability analysis and as far as we know, no author seems to have gone far the use of DPGM to represent more complex models than a Markov process with exogenous constraints as in [19].
In this article, we propose to extend the variable duration model introduced in [16] to build a comprehensive model for complex survival distributions.
Qualitative definition The proposed model, which we denote by Graphical Duration Model (GDM), is depicted in figure 2.2.5 as a 2-SPGM. This model allows describing, in a flexible and accurate way the behaviour of a complex system given its context. Indeed, three different parts are considered:
The system state (Xt) over the sequence. ZZ,..., The covariates 1,t P , t used to describe the system context. X D The duration variable t describing how long the system remains in a specific state.
Moreover, a transition variable (Jt) is added to explicitly characterise when the system jumps into another state. Indeed, if Jt=1, it means that the system state will change at time t+1. On the other hand, while Jt=0, the system remains in the same state. This variable is not necessary but appears to be convenient for further generalization and Conditional Probability Distributions (CPDs) definition. In addition for the
ZZ1,t,..., P , t sake of readability, we denote by Zt the random variable vector and by zt an observation of Zt,
zt z1, t,..., z P , t in other words with zP,t an observation of the variable ZP,t .
Figure 2.2.5: Representation of a GDM.
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Then, it is possible to factorise the joint probability distribution of the variables Xt,XtD,Jt, Z over a sequence of length T as it follows
Besides, in this model the system state transition depends on the duration spent in the current system state and the current state itself. Thus, we are in a discrete semi-markovian approach [2][3]. Indeed, we can specify any kind of state sojourn time distribution by contrast with a classic markovian approach in which all durations have to be exponentially distributed.
This modelling is particularly interesting since it allows taking into account complex degradation distributions and context effects at the same time.
CPDs definition The following paragraph addresses the specification of each CPD involved in equation (3) characterising the joint probability distribution in a Graphical Duration Model (GDM).
Covariates PDFs
We suppose that each covariate Zp takes its values in the set p, so that Zt is defined over the set
Z=Z1x...xZP. As the covariates do not have any parent in the model, their Probability Distribution Function (PDF) is not conditional and for each p we have:
For instance, suppose that we are studying a component which is considered to be only subjected to
its type of functioning speed ("slow", "normal", "fast"). In this case, there is only one covariate Z1. Its
PDF could be represented as a table (or vector) with three elements slow, normal and fast specifying the different proportions of using types.
System state CPDs
We make the assumption that the number of system states is finite and let S s1,..., sK be the set of the K different states. The first CPD concerns the distribution of the initial system state according to its context:
where zp )( is a vector of K elements depending on the vector of values z1. X1
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The second state CPD concerns the dynamic transition from one state to another. As a transition occurs at time t if and only if the variable Jt-1=1, we have
where A(zt) is a stochastic matrix of size KxK depending on the covariate values zt. In general, A(zt) is named the transition matrix of the system.
On the other hand, if Jt-1=0, the system remains in the same state. Therefore, the CPD is deterministic and the transition matrix has to be equal to identity:
Duration CPDs
The first duration CPD describes the sojourn time distribution for each state and each combination of
p D covariates. We denote by X this conditional duration distribution and we have:
p(,,) d i z where X D t represents the probability to stay during d time units in the state si given the context zt. Besides, as we are studying discrete-time models, the duration unit d is a non negative p(.,., z ) integer. XD t can be seen as an infinite matrix (along its first dimension) depending of covariates values zt.
In practice, it is possible to set an upper time bound D so as the time scale becomes finite. Indeed in p(.,., z ) this case, d{1, …, D} and XD t is a finite matrix of D x K elements.
The dynamic duration CPD aims to memorize the time spent in the current state. Indeed, if the previous remaining duration is greater than one, we update the remaining time by deterministically decreasing it by one unit.
If the previous remaining time reaches the value one, a transition occurs at time t and the duration in
p D the new current state is drawn according to the CPD X . In other words,
D Xt1 1 J 1 Let us note that the case and t 1 is not consistent. As a consequence the previous CPD is undefined for these values. We can illustrate the duration CPD in the case of two discrete covariates
pX D and geometric duration distributions. Then, is a parametric CPDs defined for any (d, i, z1, z2) by
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with θ (i, z1, z2) the geometric distribution parameters for each state si and each pair of covariate
values z1 and z2.
Finally, it is worth noting that the discrete-time assumption laid on duration distributions by the modelling can be easily overcome. Indeed, authors in [5] present a survey of discrete lifetime distributions and describe some of them which come from usual continuous ones (e.g. exponential, Weibull).
Transition CPD
Jt is a random variable characterising the occurrence of a system state change at time t. More
precisely, when Jt=1, a transition is triggered at time t+1 and the state remains unchanged while Jt=0. Besides, a transition occurs at time t+1 if and only if the remaining duration in the current state at
time t equals one. As a consequence, the CPD of variable Jt is deterministic and defined by
RELIABILITY ANALYSIS USING GDM
Basic definitions In this section, we suppose that the set of system states S is partitioned into two sets U and D (i.e. S=UD with UD=), respectively for "up" states and for "down" states (i.e. OK and failure situations). The system transition matrix from equation (3) can be decomposed as follows:
The four sub-matrices introduced in the previous equation allow to specifically describing the transition rates between up and down states. Typically, in a reliability study without maintenance action, it is impossible to go back into an up state if the system reached a down state (except for self reparable A., z ,. system). In this paper we assume that the matrix DU is equal to zero.
Reliability Let R: N* → [0,1] denote the reliability of the system. R(t) represents the probability that the system is always stayed in an up state until moment t. In other words,
Similarly, let TD denote the random variable describing the first hitting time of the subset D, i.e. T inf t * X D D t and then the reliability is given by
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Although the reliability is supposed to be undefined for t=0, we set that R(0)=1 by convention which is useful for the definitions given in the sequel. A z 0 Finally, we can remark that in the case DU (i.e. D is a set of absorbing states), we have
Failure rate The failure rate h: N* → [0,1] is defined as the conditional probability that the failure of the system occurs at the moment t given that it has worked until moment t-1. In other terms,
Besides, the failure rate can be expressed using the reliability as follows:
Mean Time To Failure (MTTF) The Mean Time To Failure (MTTF) is defined as the expectation of the lifetime (i.e. the expectation of the hitting time to "down" states D):
Once again, it is possible to express the MTTF with the reliability:
Conclusions As the failure rate and the MTTF can be expressed using the reliability, the objective is to build an algorithm able to compute R(t). The simplest approach consists in using a generic graphical model inference method like those based on junction trees. Unfortunately, these kinds of methods are not optimized for the problem of reliability estimation since they involve extra-calculations (e.g. junction tree building, backward probability propagation) which are not necessary for our problematic. That is why in the next section, we propose an efficient and simple algorithm aimed to estimate the probability of any sequence of state subsets d efined as }}, where each T S with S, the set of the system states.
Thus, by setting UU,..., , the method will provide R(t). t times
Besides, let us note that exact calculations can be carried out provided all the CPDs in the model are finite and discrete (i.e. represented as CPTs). Otherwise, one can resort to use approximate inference algorithms which allow in general working with any kind of CPDs.
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ESTIMATION METHOD D By analogy with the Markov property, it is straightforward to verify that in a GDM, the pair (,)XXt t d- separates the future (slices t+1) from the past (slices t-1 1). In other words, the future is D independent from the past given (,)XXt t which is noted:
As it is shown in the next paragraphs, this property is the key to make tractable calculations in GDMs.
The aim of the following paragraph is to build an algorithm able to compute the probability:
D To begin, lett(i , d ) P X1 1 ,..., X t 1 t 1 , X t i , X t d , then using the DGM joint distribution factorization, we obtain:
where z=(z1, …, zp). As a consequence, from the previous equation, we deduce the initial probability to begin in the subset of states 1:
Besides, we can write:
D Observing that marginalizing onto variables ZXJ ,, 1 1 lets the term C1 unchanged and sums to 1 t 1 one the term C2, it follows:
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Hence using this result, we can express t as a function of t-1 since we have:
In addition for the sake of readability, let mt ( j , d ', i , d ) denote the quantity:
such that equation t(i,d) can be rewrite as follows:
Finally by definition of t, we find that:
To sum up, theses results show that given any state sequence={1, …, T}, the following forward recursion allows to compute the probability of the sequence :
Some aspects about the behaviour of the previous recursion are discussed in the three following remarks:
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Under the classic assumption according to which all the CPDs are identically distributed over time as soon as t2, then mt does not change during the recursion. Thus, it is possible to compute mt once and for all which decreases the algorithm computing time.
If all the CPDs are finite and discrete (i.e. represented as CPTs), then integrals over the Zp’s and infinite sums over N* become finite sums which allows to perform exact calculations.
1 2 1 For instance, if we set {UU ,..., } , and {SS ,..., , } respectively, then the previous method will t times t1 times compute R(t) and PX t t respectively.
APPLICATION TO TRACK RELIABILITY ESTIMATION Nowadays, the increasing of traffic and axle loads has lead to a rail breaks growth. For safety reason, restrictive exploitation rules were defined (a train can run on a breaking rail but only after an enforcement process and with low speed) increasing delays and then, diminishing the service quality. Moreover, expensive corrective maintenance costs are needed to make up for this kind of failure.
Therefore, efforts are being made for the application of reliability-based and risk-informed approaches to maintenance optimisation of railway infrastructures. The underlying idea is to reduce the operation and maintenance expenditures while still assuring high safety standards [18].
In this application, we will focus on the reliability analysis of the rail and let maintenance modelling for further works.
Variables definition Let define the meaning of the different variables involved in the GDM considering our railway case study.
Z1,t represents the type of the material installed in the studied track section: "homogeneous rail" (R),
"welding" (W) and then Z1={R, W}.
When a serious damage is detected, maintenance operators proceed to a local rail renewal. To that end, they perform an aluminothermic welding which leads to two welding joints on the rail section tips. As the welding lifetime is lower than the rail lifetime, most of new damages occur around the formers. As a consequence, the more welding are installed, the weaker the global reliability of the studied track is.
Xt is the state of our system, namely the studied rail track between two stations (in our application we consider the inter station “Gare de Lyon-Nation”). We consider three states of degradation: "no defect" (N), "minor defect" (D), "critical failure" (F) and then S={N, D, F}.
The first two states do not bring on service disturbances or safety problems like the last one. That is why we set U={N, D} and D={F}.
D Xt is the duration variable. In this case, we set the duration unit to be the month.
As all the variables take finite and discrete values, it is possible to use an exact inference algorithm to compute the track reliability and related metrics over time.
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CPDs learning Feedback experience databases are used to estimate the CPDs parameters using the statistical method presented in equation (2).
Table 1 gives an extract of the database used as input of the learning process. Each entry of this database represents a change of the considered track state. For each change (i.e. each entry), the following information are available:
The context at which the change occurs. In this example, only the singular point (rail/welding) is considered.
The state of the track before the change (state t).
The duration spent in the state before the change.
The new state after the change.
For instance, the first entry shows that a welding (W) part of the considered track is stayed 23 months without any defect (N) until a minor defect (D) appeared. The last entry illustrates the case of a critical failure (F) occurring on a rail which spent 77 months in a healthy state (N).
From these feedback experience observations, the two main groups of parameters (i.e. the transition tables and the duration distributions) will be estimated.
Singular point State t Duration (month) State t+1 WN 23 D WD 1 F WN 10 F RN 77 F Table 2.2.3: Exploitation of feedback experience databases
Learning results concerning the duration CPDs are depicted in figure 2?2.6. These histograms represent for each singular point, the probability to stay a certain duration given the system is entered in a certain state. For instance, let consider a rail which has just jumped in the healthy state (e.g. after a renewal), then the upper left subfigure shows that the considered rail has a high probability to stay between 20 and 40 months before a change. On the other hand, the upper right subfigure considers the case of a welding of which the duration before a change has a high probability to value between 5 and 20 months.
Consequently, these results allow quantifying the well-known fact that a welding is less resistant than a rail.
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Figure 2.2.6: Histograms representing the duration CPDFs for state N.
Tables 2.2.4 give the learning results for the transition tables of the system according to its context (rail/welding). Therefore, each table sets out the probabilities that the system goes to a certain state from an initial state during a change given a specific context. For example, in the case of a welding, the right sub-table indicates that the system goes directly in a critical failure state (F) 68% of time whereas the system transits through a degraded state (D) 32% of time.
We can note that from a “healthy state” it is more probable to reach directly a critical failure without having detected a minor defect.
Indeed, this phenomenon makes difficult the application of preventive maintenance policies since preventive decisions are usually taken when the defect is still minor.
Table 2.2.4: System transition CPTs N (i.e. A(.,.)).
In the next section, we present some results obtained when combining all the knowledge contained in the local CPDs in order to compute the considered track reliability.
Results The model developed and applied during this first year has been implemented in MATLAB® environment, completed by the free Bayes Net Toolbox (BNT) written by Kevin Murphy [15]. Exact inference algorithm [8] has been used to compute reliability since all the CPDs can be represented on
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table (see figure 2.2.7(a)). Then, failure rate and MTTF have been deduced based on reliability estimations and depicted in figures 2.2.7 (b) and 2.2.7(c) respectively.
These figures allow characterising the behaviour of the studied system. As a consequence, useful information can be deduced from such analysis in order to set up and optimize reliability-based maintenance policies.
Figure 2.2.7 (b) Failure rate as a function of the welding Figure 2.2.7 (c) MTTF as a function of the welding rate. proportion.
Figure 2.2.7: (a) Reliability as a function of the welding rate.
CONCLUSIONS AND PERSPECTIVES The WP2.2.2.a aims at reducing the unavailability of tracks, setting up an optimal predictive maintenance strategy. It is therefore necessary to determine the optimum cycles of intervention to reduce the costs of the maintenance. For that purpose, the Diagnostic and Maintenance team from LTN INRETS laboratory uses to develop maintenance simulation tools based on the knowledge of the degradation processes of the component.
The chosen application concerns the rail maintenance of RATP RER tracks.
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The task was divided in three main phases: the modelling of the process of degradation of the rail, the modelling of the maintenance and, finally, the optimization of maintenance policies.
Within the first twelve months of the project, the process of rail degradation was modelled by an original probabilistic graphical approach (i.e. bayesian networks). The proposed method based on the GDMs aims to study the behaviour of any complex system. Our approach turns to be a satisfying and a comprehensive solution to model and estimate reliability. Indeed, the proposed modelling is generic since it is possible to take into account the context of the system along with an accurate description of its survival distribution. So, even if all results are introduced in a RATP context, the extension of our approach to whatever kinds of urban tracks can be easily done, since all knowledge describing the track is available.
In addition, as the method is based on graphical models, it makes it more intuitive and readable than more theoretical models.
The encouraging results obtained in this first year of the Urban Track project confirm that GDMs are competitive reliability analysis tools for practical problems. Nevertheless, results introduced in this report are limited to the rail maintenance of one specific inter station. But, it is extendable to any other track, other component… provided feedback experience data are available for the system we want to analyse.
Next step will address the problem of maintenance modelling, with the aim to build different reliability- based maintenance models which rely on GDMs. Later on, focus will be put on the development of optimisation method in order to determine optimal maintenance policies. Then, the final tool could be used as help to decisions by the people in charge of the maintenance of the track to evaluate the economic performance of the new cycles of various maintenance operations with respect of safety considerations. (a) References
[1] T. Aven and U. Jensen. Stochastic Models in reliability. Number 41 in Stochastic Modelling and Applied Probability. Springer, 1999.
[2] V. Barbu, M. Boussemart, and N. Limnios. Discrete time semi-markov processes for reliability and survival analysis. Communication in Statistics - Theory and Methods, 33(11):2833–2868, 2004.
[3] V. Barbu and N. Limnios. Nonparametric estimation for discrete time semi-markov processes with applications in reliability. Journal of Nonparametric Statistics, to appear.
[4] H. Boudali and J. B. Dugan. A discrete-time bayesian network reliability modeling and analysis framework. Reliability Engineering & System Safety, 87(3):337–349, March 2005.
[5] C. Bracquemond and O. Gaudoin. A survey on discrete lifetime distributions. International Journal on Reliability, Quality, and Safety Engineering, 10(1):69–98, 2003.
[6] D. R. Cox. Regression models and life-tables. Journal of the Royal Statistical Society., 34(2):187–220, 1972.
[7] R. Donat, L. Bouillaut, P. Aknin, Ph. Leray and D. Levy, A generic approach to model complex systems reliability using dynamic graphical models, Mathematical Methods in Reliability, Glasgow, Ecosse, Juillet 2007.
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[8] A. Gelman, J. B. Carlin, H. S. Stern, and D. B. Rubin. Bayesian Data Analysis. Texts in statistical Science. Chapman & Hall/CRC, second edition, 2003.
[9] C. Huang and A. Darwiche. Inference in belief networks: A procedural guide. International Journal of Approximate Reasoning, 15(3):225–263, October 1996.
[10]F. V. Jensen. An introduction to Bayesian networks. Press, U. C. L., 1996.
[11]J. D. Kalbfleisch and Prentice R. L. The Statistical Analysis of Failure Time Data. Second Edition. Wiley Series in Probability and Statistics. Wiley, 2002.
[12]R. Kay. Proportional hazard regression models and the analysis of censored survival data. Applied Statistics, 26(3):227–237, 1977.
[13]H. Langseth and L. Portinale. Bayesian networks in reliability. Reliability Engineering & System Safety, In Press, Corrected Proof, 2006.
[14]N. Limnios and G. Oprisan. Semi-Markov Processes and Reliability. Statistics for Industry & Technology. Springer, 2001.
[15]K. P. Murphy. The bayes net toolbox for matlab, 2001.
[16]K. P. Murphy. Dynamic Bayesian Networks: Representation, Inference and Learning. PhD thesis, University of California, Berkeley, 2002.
[17]Richard E. Neapolitan. Learning Bayesian Networks. Prentice Hall, April 2003.
[18]L. Podofillini, E. Zio, and J. Vatn. Risk-informed optimisation of railway tracks inspection and maintenance procedures. Reliability Engineering and System Safety, 2005.
[19]P. Weber and L. Jouffe. Reliability modelling with dynamic bayesian networks. In 5th IFAC Symposium on fault Detection, Supervision and Safety of Technical Processes, Washington D.C., USA, June 2003.
2.3. ADVANCED MAINTENANCE STRATEGIES (WP2.3 DEVELOPED BY TTK)
The main objective of this work package was to define a list of recommendations on how experiences from maintenance need to be taken into account when constructing new track sections or when implementing new systems.
2.3.1. Introduction
The introduction of essential maintenance aspects in the design/construction phase is quite new for European tramway networks today. In the past years, few were the number of call for tenders for the tram infrastructure construction that included a thorough chapter of future maintenance of the future tram infrastructure. More often than not maintenance aspects are neglected during these important phases of design and construction. This is, however, a necessary step that will need to be applied by
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European track networks today in order to avoid unnecessary higher maintenance costs due to insufficient design or poor construction materials or methods.
This work package searches to study the organisational aspects of track management and particularly the link between design/construction and operations/maintenance. The final objective of this deliverable is to present a list of recommendation and of best practice examples in relationship to the way the maintenance department within an urban transport operator or separate maintenance company is handling its resources.
Within this sub-project, the following questions were addressed:
What are the key maintenance questions that need to be addressed before construction?
How can the renewal of different track elements be optimised?
What are the best communication channels between the construction and the maintenance department that will considerably improve track maintenance?
2.3.2. Methodology
This work package consisted in two main activities:
Research of European and national framework of regulation regarding construction and maintenance of tramway infrastructure
Interviews with selected European Tramway operators:
Identification of the principal organisational schemes of tram management,
Selection of European Operators for surveying,
Results of the interviews,
Conclusions
Eleven light rail track networks were selected. The sample chosen is constituted of three state-owned networks (all-in-house activities), four networks where the main activities of design, construction, operation and maintenance are semi-segregated (i.e. one transport authority and one public transport company in charge of at least two of the main operations: operation and maintenance, or of all main operations: construction-operation-maintenance) and three networks characterized by having complete segregation of main activities (one transport authority, several construction design and construction consortia, one or several operators and one or several maintenance contractor).
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Begin of Operator/ Tram City tramway maintenance Type of organisational scheme Date network operation contractor survey
Red line & Complete segregation of phases/activities: RPA(RailwayProcurement LUAStram Agency) transport authority; various construction and design consortia; June 28th -29th 1. Dublin green line: Alstom/ Veolia lines Veolia - tramoperator; Alstom- vehicle and infrastructure maintenance 2007 2004 contractor
Since 1900 70 km city All-in-house activities: VBKVerkehrsbetriebe Karlsruhe (100%city 2. Karlsruhe (electric VBK August 22nd 2007 owned owned) carries out all activities tramway)
Two separate tram Complete segregation of phases/activities: Autoritat del Transport T3: 2004; T4: networks: TramBaix Metropolità (ATM): transport authority; various construction and design 3. Barcelona T1-T5 Nov 22th 2007 2004; T5: 2005 (T1, T2, T3) and Tram consortia (FCC-Vivendi, Comsa y Acciona-Necso), various tram Besos (T4 and T5) operators: Soler i Sauret, Sarbus and Connex
Semi-segregation of phases/activities: Consorcio de transportes del Area de Sevilla: transport authority; Metrocentro: in charge of operation and 4. Sevilla 1 tramline 2007 Metro Centro maintenance (partially); CAF- vehicle constructor and maintenance Nov 20th 2007 contractor; Thyssen Group, ASVI, Siemens and Sedra infrastructure constructor and maintenance contractor
T1: 1992; Semi-segregation of phases/activities: STIF (Syndicat des Transports 5. Paris T1, T2, T3, T4 T2:1997; T3: RATP d'Ile de France): transport authority; various construction and design Jan 16th 2008 2006; T4: 2006 consortia; RATP: tram operator and in charge of maintenance
Since 1891 Prague Public Transit 500 kmof All-in-house activities: Prague Public Transit Co. Inc (100%city owned) 6. Prague (electric Company (Dopravni April 28th 2008 tracks carries out all activities tramway) podnik)
20km of newlight Jan. 07, 2008- rail between begin of construction 7. Bergen (New) Bergen's centre and - inauguration Not decided Noavailable information at the moment April 29th 2008 Bergen's airport expected in 2010
(Until 2008 operated by Complete segregation of phases/activities: TFL (Transport for London) London Tramtrack Croydon Ltd integrated bodyresponsible for London's transport system; various 8. London 2000 construction and design consortia; TCLas the owner of TRamlink has a Feb. 12th, 2009 Tramlink (TCL)) Since then by TfL 99 year concession. First Group - tramoperator; TCL- infrastructure London Rail maintenance and Bombardier Transportation - vehicle maintenance
A: 1994; B: Semi-segregation of phases/activities: CUS(Communauté Urbaine de 2000; C:2000; Strasbourg): transport authority; CTS (Compagnie des Transports 9. Strasbourg 4 tramlines CTS Mai 12th 2009 D: 1994; E: Strasbourgeois): in charge of operation and maintenance (concession 2007 contract: 1990-2020)
Since 1894 10. Flemish Tram(128,3 (electric DeLijn All-in-house activities: run by the Flemish government in Belgium June 23rd, 2009 Region km) tramway)
Semi-segregation of phases/activities: SYTRAL (Syndicat mixte des T1: 2001; T2: Transports pour le Rhône et l'Agglomération Lyonnaise): transport 11. Lyon TCL Keolis July, 2009 2001 authority; various construction and design consortia; Keolis: tram operator and in charge of maintenance
Typeoforgnisationalscheme: Interviewsexecution: All-in-houseactivities duringthefirstyearofresearch semi-segregationofactivities duringthesecondyearofresearch Completesegregationofactivities duringthethirdyearofresearch
Tab. 2.3.1: Selected networks surveyed
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2.3.3. Conclusions
After carrying out eleven interviews with different European tram operators, all with very different organisational schemes of transport management, we can present the following conclusions:
Importance of a tool of internal maintenance knowledge: the real knowledge of the tracks’ conditions is being held by a reduced number of personnel (tracks’ conditions and development).
Keeping good channels of communication between the maintenance and the construction department: The closer the relationship between the maintenance and the construction department the better it is for implementing accurate maintenance plans and for producing more efficient track design.
Different organisational schemes produce different overall public costs (construction + operation + maintenance): The way of conceiving public transport services VARIES CONSIDERABLY according to the organisational scheme chosen. For each scheme different human, technical and financial resources are required. Each scheme has its advantages and disadvantages regarding overall costs, level of transparency and level of implication and responsibility of the contracting authority.
General tendencies regarding track management The tendency of externalising all responsibilities regarding tram operations and track management is reversing in some European countries. Old questions seem to arise once again regarding the advantages and disadvantages of state-owned companies and private companies of urban transport services and regarding the exact role of transport authorities in assuring public transport services.
In general two major tendencies regarding coordination and direction of main transport activities are identified in the discussions with the operators:
The operators, within in-the-house operations organizations and usually being 100% public owned, assure directly the major tracks of overall control and coordination. The transport authorities have in charge of all main activities of design/construction, operation and maintenance, they decide which activities to externalise but they keep control of these activities at all times (examples of such schemes: Karlsruhe, Prague and De Lijn).
The transport authorities coordinate themselves all the different contracts with the respective companies in charge of construction, operations and maintenance or deals directly with one consortium in charge of all main activities. (BOT – Build, Operate and Transfer – schemes; examples of such schemes: Dublin, London – before 2008 and Barcelona).
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