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UIC CODE 2nd edition, September 2010 Translation

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Recommendations for the design of bridges to satisfy track requirements and reduce noise emissions Recommandations concernant la conception des ponts pour tenir compte des exigences relatives à la pose et à l’entretien de la voie et pour réduire les émissions de bruit Empfehlungen für die Konstruktion von Brücken unter Berücksichtigung oberbautechnischer Anforderungen und zur Abminderung der Schallemission

Leaflet to be classified in Volume:  VII - Way and Works

Application: With effect from 1 July 1995 All members of the International Union of Railways

Record of updates 1st edition, July 1995

First issue

2nd edition, September 2010

Computerisation of Leaflet (1st edition, July 1995). NB: the contents of the July 1995 edition have not been changed.

The person responsible for this leaflet is named in the UIC Code

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Contents Summary ..............................................................................................................................1 1-

Introduction ................................................................................................................. 2

2-

Requirements for trackwork across bridges............................................................ 3 2.1 - Introduction ........................................................................................................... 3 2.2 - Vehicle and operating requirements ..................................................................... 3

3-

2.2.1 -

Introduction ........................................................................................................ 3

2.2.2 -

Means of ensuring track continuity .................................................................... 3

2.2.3 -

Direct track fixing ............................................................................................... 4

2.2.4 -

Operating requirements ..................................................................................... 5

Case of steel bridges .................................................................................................. 6 3.1 - Introduction ........................................................................................................... 6 3.1.1 -

Accessibility ....................................................................................................... 6

3.1.2 -

Maintenance operations..................................................................................... 6

3.1.3 -

Requirements for mechanised track maintenance............................................. 6

3.2 - Track maintenance ............................................................................................... 6 3.3 - Maintenance of the structure ................................................................................ 7 3.4 - Requirements for ballasted track .......................................................................... 7 3.4.1 -

Depth of ballast below sleepers ......................................................................... 7

3.4.2 -

Protection of the bridge-deck waterproofing ...................................................... 7

3.4.3 -

Enclosure of ballasted decks ............................................................................. 7

3.5 - Components at the ends of a bridge..................................................................... 8 4-

Measures to reduce noise and vibrations ................................................................ 9 4.1 - General comments on noise generation............................................................... 9 4.1.1 -

Sources of noise ................................................................................................ 9

4.1.2 -

Noise produced by rolling stock ......................................................................... 9

4.1.3 -

Noise emitted by the track ................................................................................. 9

4.2 - Transmission of vibrations and radiation of noise................................................. 9 4.2.1 -

General .............................................................................................................. 9

4.2.2 -

Transmission of vibrations ............................................................................... 10

4.2.3 -

Radiation of noise ............................................................................................ 10 717 R

4.3 - Measures to limit the generation and radiation of noise ..................................... 10 4.3.1 -

Main requirements ........................................................................................... 10

4.3.2 -

Basic principles ................................................................................................ 11

4.3.3 -

Measures specific to the track ......................................................................... 11

4.3.4 -

Measures specific to the supporting structure ................................................. 12

Appendix A - Ballasted track laid on steel bridge .......................................................... 13 Appendix B - Ballasted track on reinforced concrete bridge ........................................ 14 Bibliography .......................................................................................................................15

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Summary This leaflet contains relevant guidelines for the design of railway bridges in order to meet traffic requirements, given the need to minimise not only track maintenance work but more importantly track maintenance on bridges and their abutments. The importance of reducing noise levels is also highlighted. The leaflet recommends that bridge design should also allow for longidudinal forces emitted via the rails, and caused by temperature variations or on train braking or again during initial acceleration. Details are also given of the measures to be adopted as regards: -

the thickness of ballast under sleepers;

-

the enclosure of ballasted bridge decks.

The appendices to the leaflet provide examples of ballasted-track laying on concrete or steel bridges, complete with recommended dimensional values.

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1 - Introduction The construction of new bridges must take account of requirements for the installation and maintenance of permanent way that will be laid across them. It is also recommended that the design of any new bridge should include appropriate measures for limiting the radiation of noise and vibration to satisfy environmental requirements. When continuous welded rail is laid across the bridge, longitudinal forces are generated either by thermal variations in the bridge supports or braking/ traction forces on the bridge itself, and these are partly absorbed via the track and partly by the sub-structure. These forces must be taken into account and calculated into bridge and bridge-support design. This leaflet concerns ballasted track on concrete (see Appendix B - page 14) or steel (see Appendix A - page 13) bridges. Cases of ballastless track/slab track are also introduced. This document should be used in conjunction with the following UIC leaflets (see Bibliography page 15): UIC Leaflet 776-1

Loads to be considered in railway bridge design

UIC Leaflet 776-2

Bridges for high and very high speeds

UIC Leaflet 776-3a

Deformation of bridges

UIC Leaflet 719

Earthworks and trackbed construction for railway lines

UIC Leaflet 774-3

Track - bridge Interaction. Recommendations for calculations

a. Will be suppressed after publication of 776-1 and 776-2 new editions and EN 1991-2 & EN 1990 A1

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2 - Requirements for trackwork across bridges 2.1 -

Introduction

Track requirements in relation to a bridge should take account of the following criteria: -

the requirements of the type of rolling stock which will run over it;

-

the need to limit maintenance of the track both over and adjacent to the bridge, and the maintenance of the bridge itself,

-

all restrictions with regard to structural height,

-

the need to limit environmental nuisance from noise emissions to an acceptable level.

These requirements are summarised below, listing the main technical criteria to be met.

2.2 2.2.1 -

Vehicle and operating requirements Introduction

It is important to ensure continuity of the track so as to contain the dynamic forces within acceptable limits for the running speeds and axle-loads concerned. The behaviour of the "track/bridge" system should be as close as possible to the behaviour of the "track/ formation" system, and any transition between the two systems should be gradual and uniform. Ideally, rail traffic should not "notice" the bridge. This is generally the case where bridges are provided with a ballast bed, so that the track characteristics on the bridge and on formation are identical, and the stipulated deformation values are not exceeded.

2.2.2 -

Means of ensuring track continuity

The following means are used to satisfy the various requirements placed on the track. 2.2.2.1 -

Rail continuity

Expansion joints at the ends of the structure should be avoided wherever possible and the use of continuous welded rails (CWR) across the structure is recommended. In case of continuous welded rails, a check should be made to ensure that the profile of the ballast gives a track stability (resistance to lateral displacement) not inferior to its correspondent on formation. Rail joints (including bonded insulated joints or track expansion joints) should be located wherever possible so as not to occur within 2,5 m of the ends of the bridge - over the abutments on the embankment side - or in continuous spans, within 2,5 m of the centre-lines of the piers.

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2.2.2.2 -

Continuity of the track system

Wherever possible the bridge should be designed to accommodate similar track construction to that which is laid on the embankment approaches. The use of ballasted track on the bridge is one of the most effective means of ensuring track uniformity. The ballast may be supplemented, if necessary, by a resilient mat between ballast and bridge deck for the purpose of reducing the stiffness of the track support, and to give the track over the bridge a vertical stiffness similar to that on the adjacent embankment. At the ends of the bridge, precautions should be taken to prevent the ballast from encroaching on the bridge bearings. A means of retaining the ballast should be incorporated into the design of the bridge deck, to ensure that the ballast profile is maintained. With large expansion lengths (> 100 m) and expansion joints, provision should be made for a discontinuity in the ballast bed, in order to avoid ballast movement in the transition zone, where the expansion length makes this possible. Direct fixing of the rails to the bridge deck should be limited to special circumstances where ballasted track cannot be accommodated (e.g. because of restricted structure height or on emergency bridges). 2.2.2.3 -

Continuity of alignment

In designing the bridge, the alignment and level of existing railway tracks should be carefully recorded so that the optimum layout of the line is retained even after the bridge has been constructed. 2.2.2.4 -

Transition between formation and bridge

The design of the bridge should ensure a smooth transition between the formation and the bridge to avoid any hard spots. A number of suitable backfilling options are given in UIC Leaflet 719, point 2.3.5, and it is suggested that reference should be made to this document for guidance in selecting a suitable backfill. The abutments should be constructed as closely as possible at right-angles with the line of the track so as to minimise the risk of track twisting under traffic.

2.2.3 -

Direct track fixing

Where limitations of structure height prevent the use of ballasted track, it will be necessary to adopt a method of direct rail fastening. The design of the direct rail fastening should ensure that the stresses and vibrations due to rail traffic are adequately catered for. This is usually achieved by attaching rail baseplates, sleepers or rail bearing blocks directly to the deck. Particular attention should be given to ensuring accurate track alignment. The direct rail fastening system should ensure a certain degree of elasticity in order to prevent forces from becoming so high that failures in the rail fastening could occur.

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Another option for direct fastening is to position the rail accurately in troughs incorporated into the design of the bridge deck, and then locate them in position by filling the troughs with an elastomer compound. Such a system cannot deform plastically and is therefore suitable only for short spans (up to 20 m) or where an expansion device is provided at both ends of the bridge. If it is intended to use directly-fastened track in conjunction with continuous welded rail, and allowing for interaction forces, it will be necessary to carry out tests under the full range of operational and climatic condition so as to determine values for the longitudinal resistance of the track, which will be valid for the anticipated life of the structure, for use in the design calculations. Generally, only abutments constructed at right-angles with the track are permissible with direct rail fastening.

2.2.4 2.2.4.1 -

Operating requirements Avoidance of disruptions to traffic

The bridge should be so designed that traffic interruptions for maintenance work are kept to a minimum. Maintenance of the track will be minimised if the recommendations of point 2.2.2 - page 3 are followed. 2.2.4.2 -

Provision for future development

A new bridge should not restrict the clearance gauge for vehicles operating over the system, and it may be appropriate to allow additional clearance for possible enlargement of this gauge. 2.2.4.3 -

Protection of bridge structures

The consequences of a derailment on a bridge can be serious. Each railway must therefore specify the necessary safeguards against this risk. The rules in force stipulate the derailment loads to be taken into consideration. Where guard rails are used, they should be fitted in such a way that, whilst providing effective guidance for derailed wheels, they do not hamper mechanised track maintenance (tamping machines). In the case of track laid on reinforced concrete or on steel deck, these safeguards can be dispensed with when the deck edge is at a higher level than that of the sleepers, and if it is robust enough to provide wheel guidance. 2.2.4.4 -

Safety of staff

Walkways for staff carrying out maintenance work should be positioned at an adequate distance from the nearest track, both horizontally and vertically, in compliance with local regulations.

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3 - Case of steel bridges 3.1 -

Introduction

Track and bridge-support maintenance is expensive and the structures should therefore be carefully designed to minimise the maintenance costs involved

3.1.1 -

Accessibility

Access routes or walkways of sufficient width should be provided to enable maintenance staff to cross the bridge safely. Hand-rails are an essential safety feature and should be installed on all walkways. Access to the bridge from the embankments should also be considered from the safety standpoint. Elements obstructing visibility should be eliminated as far as possible. Installations running parallel to the track (cable, pipes, etc.) should also be accessible for maintenance without the need to encroach on the clearance gauge.

3.1.2 -

Maintenance operations

The provision of continuity as described under point 2.2.2 - page 3 also leads to a reduction in maintenance costs through the elimination of various items (e.g. rail joints or expansion joints), so that uninterrupted mechanised maintenance can be carried out.

3.1.3 -

Requirements for mechanised track maintenance

A ballasted track system enables mechanised maintenance to be used, which is advantageous in term of quality, ride and cost effectiveness. Ballasted track should therefore be used wherever possible. However, in order to maximise the benefit of mechanised maintenance, adequate clearance must be provided for both machines and personnel, with a sufficient ballast depth to protect the bridge deck and any protective layer from accidental damage.

3.2 -

Track maintenance

In order to facilitate track levelling and lining, laying on ballast is preferable to direct rail fixing. Regardless of whether the track is supported on sleepers or directly fastened to the deck or to longitudinal timbers, the insertion of rail pads or baseplates will reduce the dynamic effects of shock loadings which can lead to loosening of rail fastenings and/or to an increase in the dynamic loading on the structure. Timber sleepers are sometimes used across bridges because of their lower overall height.

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3.3 -

Maintenance of the structure

Fastening systems which connect the rail rigidly to the bridge deck should be avoided whenever possible. The structure should be designed so as to avoid inaccessible areas that are exposed to corrosion or to the accumulation of dirt, as this can lead to electrical insulation problems, particularly on steel bridges. All parts of the structure (such as bearings and areas needing painting) should have good access for inspection and maintenance.

3.4 3.4.1 -

Requirements for ballasted track Depth of ballast below sleepers

In order to prevent damage to the bridge deck and its waterproofing, and also to help in maintaining a good track alignment, a minimum of 350 mm of ballast must be laid under the sleepers and any parts protruding into the deck and liable to interfere with the operation of track maintenance machines must be avoided. In carrying out track maintenance involving reballasting, it is often more cost-effective to lift the track than to dig out the old ballast. Allowance should be made in the design (e.g. by providing additional height of ballast retaining walls) for accommodating an increased depth of ballast. Provision for at least an extra 100 mm of ballast is recommended and the effect of this on the structure gauge should be considered.

3.4.2 -

Protection of the bridge-deck waterproofing

It is recommended that all bridge decks waterproofed in turn should be given a protective coating.

3.4.3 -

Enclosure of ballasted decks

In order to allow for the passage of mechanical ballast cleaner chains, a minimum distance of 2,20 m from the centre of the track to the edge of the ballast should be provided. This enables either timber or concrete sleepers to be used, with adequate clearance for maintenance work. In the case of bridges with more than one track, where each track rests on a separate structure, particular attention should be paid to the position of any ballast walls between structures so as to avoid restricting the passage of track-laying machines. Similarly, any drainage outlets from the deck should also be carefully located to prevent damage during maintenance work. Where tracks are on curve, the clearance should be increased where necessary.

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3.5 -

Components at the ends of a bridge

The ballast should be maintained at a constant depth across the bridge and on the adjacent embankments. It is important to ensure that ballast walls incorporated into the abutments do not foul the working range of track machinery. Continuous welded rail (CWR) is generally used for good track alignment and ease of mechanical maintenance and, as noted under point 2.2.2 - page 3, the components at the ends of the bridge should be so designed that the track can continue. The displacement of the structure under traffic loads should be limited so as to minimise any loss of compaction in the ballast. However, in the vicinity of the abutments, additional measures may need to be taken to safeguard the track from buckling. Adequate drainage should be provided at the ends of all bridges. Details of recommended designs for sliding bearing ends are shown below for short, medium and long expansion lengths.

Short expansion length

Medium expansion length

Long expansion length (> 100 m)

Fig. 1 - Details of sliding bearings

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4 - Measures to reduce noise and vibrations 4.1 4.1.1 -

General comments on noise generation Sources of noise

Noise from railway bridges occurs as a result of the characteristic features of both vehicles and track, and their interaction.

4.1.2 -

Noise produced by rolling stock

Natural vibrations excited by the rolling stock result from the interaction of bogies/vehicle bodies and wheelsets/bogies with the track. Those frequencies which lie in the audible range are clearly the most important, and of these the frequencies in the range between 40 and 60 Hz seem most likely to arise from vehicle characteristics, in addition to very many lower frequencies which are not acoustically significant.

4.1.3 -

Noise emitted by the track

Noise radiated from a railway bridge by passing trains will depend on the roughness of the wheel and rail running surfaces, and on variations in track support stiffness. Some of these features will be randomly distributed and will cause only occasional noise emission; others will be strictly periodic and may lead to sustained vibration. Taking a typical sleeper spacing of 600 mm, the frequencies generated by train speeds in the 50 to 300 km/h range lie between 20 and 150 Hz. If the excitation frequency in this range coincides with a non speed-dependent natural frequency of the bridge, then the bridge will generate a particularly strong response. If there is a coincidence between the frequencies due to the track and those arising from the rolling stock, significant noise emission may occur, with particular regard to the low frequency excitation of the bridge.

4.2 4.2.1 -

Transmission of vibrations and radiation of noise General

The following factors have a significant influence on the overall acoustic effect: -

train type,

-

train speed,

-

train length,

-

type of construction and length of supporting structure,

-

maintenance condition of track and wheels.

The main factors involved in the transmission of vibrations are: -

the type of track and track support (ballast bed),

-

the design of the bridge structure.

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4.2.2 -

Transmission of vibrations

During the passage of a train over the bridge, the fluctuating mechanical forces exerted by the axleloads are attenuated to some extent by the rails and their supports. In particular, these fluctuating forces produce flexural waves which result in radiation of a droning noise. This noise is particularly strong if the excitation frequencies coincide with natural frequencies of parts of the bridge structure and cause resonance, i.e. if the vibrations generated by the loaded axles lie in the same frequency range as the natural frequencies of parts of the construction. The generation of airborne noise involves three steps: -

generation of vibrations within the structure,

-

propagation of vibrations through the structure,

-

radiation, i.e. excitation of airborne noise from the structural vibrations.

4.2.3 -

Radiation of noise

The radiation of noise from a railway bridge arises mainly from the excitation of the component parts of the structure. The flexural stiffness, material and thickness of the deck plate are very important in this regard. The degree of resistance offered by the deck support to the initiation of vibrational energy (mechanical input resistance) is called mechanical impedance. The noise measured at the side of a bridge during the passage of a train consists of: -

a high-frequency noise similar to that radiated by the same train running on open track (direct radiation of airborne noise from rolling stock and rails),

-

a low-frequency noise radiated by the structure (radiation of structure-borne noise).

In the low-frequency range of the noise spectrum, measured to the side of the track, there may be a very marked difference between the noise of a train running over a bridge and running on open track, even though the difference in noise level as measured in dB(A) may be practically insignificant. For bridges with closed deck, the noise levels measured under the bridge may be attributed almost entirely to the vibration of the structure (secondary noise).

4.3 4.3.1 -

Measures to limit the generation and radiation of noise Main requirements

The objective of all measures relating to the track and the bridge structure is to ensure that, when a train runs on a bridge, the noise level generated will not be any higher than when running on open track. In order to reduce the noise radiation from railway bridges, it is essential that the natural frequencies of those parts of the bridge structure which radiate the most noise do not lie within the frequency ranges where there is strong excitation. If there is no alternative to their lying within the critical range(s), the frequencies concerned should be heavily damped, though this may be present practical difficulties.

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Fundamental steps for reducing noise and its radiation involve: -

measures specific to the track,

-

measures specific to the supporting structure.

4.3.2 -

Basic principles

The most important measures involving the deck are: -

removal of any form of discontinuity at the transition between the embankment and the bridge to eliminate any leap in resilience;

-

creation of a smooth and level rail surface. Rail joints, welds and expansion joints contribute significantly to amplify the airborne noise emitted from the bridge.

4.3.3 -

Measures specific to the track

The following points regarding construction should be taken into account: 4.3.3.1 -

Ballasted track

It is generally recommended that ballasted track should be used on bridges where there are noise problems. If necessary, an additional mat may be inserted under the ballast to give an extra reduction of noise, particularly on heavily-used lines. This reduction will be obtained both from greater track resilience because of the mat, and also possibly through greater damping of the track and the supporting structure. 4.3.3.2 -

Track fixed directly on open deck

Bridges with open decks (and in particular those with direct rail fastening) are amongst the types of bridge generating the most noise, owing to the absence of a ballast bed. Some reduction of the structure-borne noise may be obtained by insulating the deck and supporting structure through insertion of resilient pads. Such action, though, is unsuitable for reducing airborne noise. 4.3.3.3 -

Track fixed directly on closed deck

For directly-fixed track, the following measures can reduce noise: -

reduction of the level of rail-generated noise through the use of resilient rail pads;

-

reduction in vibration of the bridge elements, e.g. by incorporating an intermediate damping layer in order to separate the track from the bridge deck;

-

reduction in vibration of the bridge elements through changes in construction (e.g. by welding-in additional stays), in order to modify the natural frequencies of the bridge elements.

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4.3.4 -

Measures specific to the supporting structure

4.3.4.1 - General principles to be adopted when designing the supporting structure: -

increase the mass (e.g. by using concrete elements or extra ballast) although this is only possible where the required space for the increased depth of the ballast bed is available, and structural engineering considerations permit;

-

increase the stiffness in the region of the bridge deck and reduce the stiffness of noise-generating elements (e.g. vertical web plates and bottom plates in box girder bridges);

-

cover the noise-generating elements with a layer of material to provide additional mass or damping, or a combination of these two factors.

4.3.4.2 - Types of track which have generally proved satisfactory: -

reinforced or prestressed concrete used as a deck slab or as part of a box girder construction;

-

composite construction;

-

steel bridges with ballasted deck.

4.3.4.3 - Precautions Generally, special precautions must be taken to achieve a significant reduction in vibrations: -

the natural frequency of the individual structural elements of the bridge should be prevented from coinciding with the excitation frequencies of the bridge. The vibration of the bridge deck is of paramount importance in the transmission of vibrational energy to the other members of the structure. Consequently, the bridge deck should have a high level of impedance;

-

reinforced concrete, prestressed concrete and composite construction bridge radiate less noise and generally give rise to fewer acoustic problems than steel bridges. The difference lies in the characteristic impedance of the deck. With concrete and composite structures with a relatively bulky deck plate, this impedance is significantly higher than in steel bridges;

-

the web plates are the elements of box girders which emit the most noise. For maximum reduction of noise emission, the web plates should be made as thin and flexible as possible so that their fundamental natural frequency lies below 30 Hz. The bottom plate should also be as thin and flexible as possible, so that the fundamental frequency of the bottom plate does not coincide with that of the webs, i.e. the bottom plate should be "softer", having a lower frequency than the web plates;

-

in order to reduce the emission of noise, a "sandwich" design may be used comprising, in the area of the bridge deck, a steel deck plate, a visco-elastic synthetic mat, and a protective layer beneath the ballast bed.

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Appendices

Appendix A - Ballasted track laid on steel bridge

2 200 mm

100 mm

2 200 mm

ü

min 350 mm

1) 2%

1) High-speed lines: 400 mm

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Appendices

Appendix B - Ballasted track on reinforced concrete bridge

2 200 mm

2 200 mm

1%

ü

min. 350 mm

1)

2%

1) High-speed lines: 400 mm

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Bibliography 1. UIC leaflets International Union of Railways Leaflet 719: Earthworks and trackbed construction for railway lines, 3rd edition, February 2008 Leaflet 774-3: Track - bridge Interaction. Recommendations for calculations, 2nd edition, October 2001 Leaflet 776-1: Loads to be considered in railway bridge design, 5th edition, August 2006 Leaflet 776-2: Design requirements for rail-bridges based on interaction phenomena between train, track and bridge, 2nd edition, June 2009 Leaflet 776-3: Deformation of bridges, 1st edition of 1.1.89

2. European standards European Union (EU) EN 1990:2002/A1/2005: Eurocode - Basis of structural design, April 2006 EN 1991-2:2003: Eurocode 1 - Actions on structures - Part 2: Traffic loads on bridges, October 2003

3. Minutes of meetings International Union of Railways Way and Works Committee (Question 7.4.1 - Approval of new Leaflet 717), May 1995

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Warning No part of this publication may be copied, reproduced or distributed by any means whatsoever, including electronic, except for private and individual use, without the express permission of the International Union of Railways (UIC). The same applies for translation, adaptation or transformation, arrangement or reproduction by any method or procedure whatsoever. The sole exceptions - noting the author's name and the source - are "analyses and brief quotations justified by the critical, argumentative, educational, scientific or informative nature of the publication into which they are incorporated". (Articles L 122-4 and L122-5 of the French Intellectual Property Code).  International Union of Railways (UIC) - Paris, 2010 Printed by the International Union of Railways (UIC) 16, rue Jean Rey 75015 Paris - France, September 2010 Dépôt Légal September 2010

ISBN 978-2-7461-0644-2 (French version) ISBN 978-2-7461-0645-0 (German version) ISBN 978-2-7461-0646-9 (English version)

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