LR55 - the next generation of tramway tracks

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LR55 Frequently Asked Questions

LR55 Track System - Some questions answered
by Lewis Lesley

1.0 Introduction

A full paper setting out all the testing undertaken of the LR55 track system contains much additional information that will amplify these points. In general the perceived weakness of the LR55 track system is the strength of the bonding material which holds the rail in the concrete foundation troughs. In laboratory and field trials two competing bonding materials were tested :

The SIKA Grout had previously been tested by the University of Calgary, and the tests undertaken in Liverpool replicated and confirmed the Canadian tests. The KC330 grout was used to bond the light rail system in Calgary. The KC330 was subjected to more laboratory testing than the System 6, and the KC330 was used for the Rotherham Bus Station trial, while the System 6 was used at the Alsing Road Supertram trial. Both have similar bonding, mechanical and electrical properties. SIKA have used the KC330 for nearly 40 years in Germany for external bonding of different materials.

In all the failure testing undertaken, the PU bonds held, while the concrete foundation troughs failed in tension. Properly installed either PU grout is more than adequate for the task of holding LR55 rails in concrete troughs.

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2.0 Installing the track

2.1 Rail
2.1.1 Pre-curving
2.1.2 Rail Jointing
2.1.3 Rail destressing
2.1.4 Track Bonds
2.1.5 Axle counters
2.1.6 LR55 joint with other sections
2.1.7 Anti skid treatments
2.1.8 Installation tolerance
2.1.9 Switches and Crossings
2.1.10 Rail grinding
2.1.11 Weld build up
2.1.12 Repairing fractured weld.
2.1.13 Installation line and level
2.1.14 Steel Specification.
2.1.15 Flangeway depth.

2.2 Trough
2.2.1 Trough length
2.2.2 Trough curves
2.2.3 Insitu trough casting
2.2.4 Trough embeddment and sealing
2.2.5 Water Seepage
2.2.6 Road surface drainage
2.2.7 Trough joints
2.2.8 Trough gauging2.3 PU Grout

2.4 Pre-assembly

2.5 Installation Proceedure.

2.6 Utilities
2.6.1 Discussions
2.6.2 Diversion ?
2.6.3 Trench widths ?
2.6.4 Routines
2.6.5 HMRI Proceedure
2.6.6 Temporary Track passing loop
2.6.7 Powers

2.7 General
2.7.1 Can the rail section comply with standards?
2.7.2 Who rolls this LR55 section?
2.7.3 How much?
2.7.4 Are Switch and Crossing units available?
2.7.5 can track gauge be maintained without any gauge ties?
2.7.6 Can vertical loadings from the troughing be supported by the existing sub structure/formation?
2.7.7 Can utility repairs really be carried out under tram traffic?
2.7.8 Will the larger rail head area give rise to increased skid risk for road users?
2.7.9 I am not aware of this system being used on any existing system

2.0 Installing the track

2.1 Rail

2.1.1 Pre-curving

This is a standard proceedure which can be undertaken in many steel shops. The curve is introduced by pulling the rail between three rollers, two on one side of the rail, and the third on the otherside mid way between the other rollers. On each pass the third roller is progressive pushed further between the first two rollers. The LR55 has been factory curved down to 15 m radius, without modification. By notching the inside of the curved rail it would be possible to achieve 11m radius. In any case if transitions are to be included, factory curving is the only way to achieve the required quality and tolerance.

2.1.2 Rail Jointing

The LR55 rail has been satisfactorily flash butt and thermit welded. Thermit have developed the required mould to weld sections together in street. Flash butt welding is also possible in street. Thermit exhibited a LR55 weld on their Railtex Stand in 1997.

2.1.3 Rail destressing

Rails would normally be destressed in the rolling mill before dispatch to customers. "Jim Crow" curved girder tram rails are not normally treated prior to installation. The other question is how to stress rails to compensate for any thermal movements. This can be by laying at the neutral temperature, or applying a slight mechanical tension prior to bonding. The problems associated with rail stress in railways are hardly a problem in street tramways, where the rails are embedded. The PU Grouts tested are more than strong enough to cope with thermal movements associated with the range of temperatures experienced in the UK. Laboratory tests were undertaken between -20°C and 60°C.

2.1.4 Track Bonds

Each rail will normally be continuously welded providing longitudinal electrical conductivity. Cross overs and other point work electrically connects the two rails in in each track and two adjacent tracks. For further assurance, copper bonds can be brazed under the rail head flange or to the side/bottom of the main rail section. Such bonds are commerically available and can be used to provide continuity along each rail and between rails/tracks, and as an insurance against leakage in the case of a weld failure.

2.1.5 Axle counters

In street tramways with operation "on sight", axle counters are not used since tramcars are integral vehicles. Some systems use vehicle detectors, like magnetic loops or proprietory, eg.Philips "VETAG". These are normally installed between the running rails under the centre line of the trams, to make the location on the trams of "beacons" practical.

2.1.6 LR55 joint with other sections

This is achieved by transition rail sections, as was used for the Alsing Road installation in Sheffield. Two patterns have already been prepared LR55/80lb and LR55/bullhead. With CAD and polystyrene patterns all possible combinations of different rail sections are now easy to achieve. The transition would normally be butt welded to the LR55 and then thermit welded to the conventional rail section.

2.1.7 Anti skid treatments

Two different kind of anti skid treatment have been applied to the LR55 installation on the Supertramway in Sheffield. One is based on an aluminium silicate bonded with epoxy resin, the other is carburumdum based. Both have resisted wear equally . In practice the opportunities for motor vehicles to skid on LR55 tracks should be minimised by tram lanes, and by locating road lanes asymmetrically to tram lines where there is mixed operation.

2.1.8 Installation tolerance

This depends partly on the likely level of tram traffic, the nature of the highway pavement and the requirements of the highway authority. The running rails can wear by about 10mm before replacement. If narrow tram wheel are use this would require grinding of the rail head to remove any step edges. The non running side is rolled about 5mm lower than the running side so that the worse case difference across the groove is + or - 5 mm. The concrete foundation trough would normally be laid flush with the highway pavement.

2.1.9 Switches and Crossings

There is a drawing for a 25m radius switch and 1:2.9 crossing in the LR55 profile. Together these two elements can be used to create all the usual point works:

These are entirely compatable with the LR55 section. With CAD other radii and crossing angles can be easly achieved.

2.1.10 Rail grinding

A standard sliding or oscillating carburundum based grinder will work perfectly adequately on the LR55 section. The only modification may be the need to remove any step edges (see 2.1.8).

2.1.11 Weld build up

The standard rail head weld up technique has been used in Germany for nearly 30 years with rails embedded in KC330. There is no need to remove or replace the PU bonding, as the mass of the rail disperses the heat so that it is below 200°C at the PU bond interface. The rails would then be reground to profile (see 2.1.10)

2.1.12 Repairing fractured weld.

A full investigation of the reason for weld failure would have to be undertaken, eg.

The PU grouting would have to be removed for about 1 metre either side of the broken weld. The Thermit mould would be placed under and around the rails. If the original weld was of poor quality, then the rails would have to be pulled together. Otherwise leaving the rails in an unstressed state would ensure that the weld was not over stressed.

2.1.13 Installation line and level

The compacted bedding layer on which the concrete foundation troughs sit is the first alignment requirement. The technique for achieving that is already well established for laying concrete drainage channels in highway pavements. With the concrete foundation troughs installed, the rails pre-welded into long strings would be aligned to line, level and gauge by either:

  1. precured wedges of PU grout, supporting the rails as the PU liquid grout is injected and then bonding to the wedge pieces, or
  2. street clamps with integral laser targets, holding the rails to line, level and gauge while the first PU pour is undertaken. When set sufficient to support the weight of the rails, the clamps are removed and a second pour completes the installation.
System 1. will be labour intensive, while system 2. will require investment in the clamps but should be much faster.

2.1.14 Steel Specification.

 Normally the promoter specifies the steel quality required. There is a VDV tram rail steel spec. which is used for Ri59 and Ri60 profiles. There is also an old BS spec.

2.1.15 Flangeway depth.

Q. Why is the flangeway on the LR55 deeper than the British Standard BS 3 tramway rail?

A. It is the same as the EU Ri60 flangeway/groove, 36mm (1 & 7/16 in) wide and 50mm (1 & 15/16in) deep. The logic for this is that it will also accommodate mainline rail wheels, which have wider and deeper flanges than tram/light rail vehicles. In many EU countries there is some sharing of tracks, eg. for the movement of rail freight wagons into city factory sites, using tram tracks, and as at Karlsruhe and Saarbrucken, light rail vehicles run over main line railway tracks (not to mention San Diego), so need wider tyres and deeper flanges to negotiate railway switches and crossings. In the EU this is normally achieved by the use of a hybrid wheel profile, first developed in Frankfurt am Main, where the tyre is 135mm wide (tram 85mm main line 180mm), and the flange is 30mm deep (cv 20 and 40). To allow for rail wear, the groove has to be deeper than the flanges.

The only place in Britain where rail freight wagons shared tramway tracks was Glasgow. Here the unique track gauge of 4ft 7.75in was used, and the rail wagons ran on their flanges along the bottom of the rail groove.

2.2 Trough

2.2.1 Trough length

For drainage channels the usual trough length is 1m. 6 m was chosen for straight tracks to minimise costs. In practice the troughs being manufactured by extrusion and then cut to length, means that any length can be specied. The Rotherham bus station trial installation used three separate troughs; 2.5m, 3.0m and 5.0m without mechanical jointing, with perfect satisfaction. Road drainage channels are not normally mechanically jointed.

For maximum mechanical strength, provided that there are no rail welds co-inciding with trough joints, which could create a hinge, then simply butting the troughs and allowing the PU grout to enter the space between the trough ends and therefore bonding the troughs together should be satisfactory.

If the steel tendons in the troughs are to be used as a "Faraday Cage" then there will need to be an external electrical bonding system between troughs. Alternately a continuous Faraday cage can be laid in the trench prior to the installation of the concrete foundation trounds. This would consist of a lightweight weldmesh folded into a "U" and sat in the bedding layer, and then grouted between the highway pavement and the trough.

With the rails fully insulated from the concrete foundation troughs there will be less stray current paths (in dry weather). In electrical tests, resistivity over 1000Ωkm has been measured. This is over ten times greater than that required by HMRI. Stray currents should not be a problem in normal installations, including switches and crossings.

The longer the trough length, the less ends to settle. In standard highway drainage channels end settlement is not normally a problem. With a continuous rail bonded to and supporting the trough ends this is very unlikely to be a problem. Trough end settlement was not a problem in the Rotherham trial.

2.2.2 Trough curves

The tightest track radius is likely to be 15m. A 20 m radius trough was designed, which would accommodate rail radii between 15m and 25m. A curved trough would however be difficult and expensive to manufacture. A simpler solution will be to use straight troughs with bevelled ends, which would be cut to length according to curve radius. For example 15m radius can be accommodated in 2m long straight troughs. For radii greater than 25m, the length of the troughs would be increased. At 100m radius 6m long troughs can be used laid as tangents.

2.2.3 Insitu trough casting

The only reason to have insitu cast troughs would be for some special structural requirement on site.

2.2.4 Trough embeddment and sealing

This is standard for concrete drainage troughs and exactly the same techiques would be used. The important control is that the bedding layer is properly compacted to a CBR > 3%.

2.2.5 Water Seepage

This is controlled by proper quality control on installation. The trial length in Rotherham Bus Station did not require any seepage control measures after installtion

2.2.6 Road surface drainage

The concrete troughs edges should be flush with the highway pavement. Road surface water normally drains to the side of the carriageway into gullies. Tramway tracks would usually be near the centre of the carriageway.

2.2.7 Trough joints

The Rotherham installation had three joints exposed to traffic, which were instrumented with strain gauges. This was not a problem, even under the heavy and randomly located bus tyres which crossed, scuffed and turned over the installation.

2.2.8 Trough gauging

In a highway pavement that is not failing plastically, there is sufficient lateral strength to resist the movement of troughs, just as there is for drainage channel installations. A simple rustless steel strop on which the troughs sit, will provide adequate gauge restraint on short radius curves if further assurance is necessary.

Tramway LR55 troughs on curve

2.3 PU Grout

Two grouts have been tested:

and can be recommended for tramway application. SIKA have a full type approval for their PU Grout from Railtrack plc for railway bonding applications. SIKA also has a worldwide system of support and supply.

The only other grout in the market is Edilon "Corkelast" which is sold only as a filler, and has poor electrical resistance qualities.

There are sufficient LR55 tests and others to satisfy that either SIKA or ALH can be used.

2.4 Pre-assembly

It has been normal tramway practice over 100 years for complex layouts, eg. road junctions, to be pre-assembled in the factory to ensure that there is a proper fit prior to shipping to site for final installation.

2.5 Installation Proceedure.

A method statement has been prepared for the installation of the LR55 track system in highway.

2.6 Utilities

2.6.1 Discussions

All the national Utilities were invited to a Seminar held in Sheffield in Sept, 1994 to explain the LR55 system and to inspect the Rotherham Bus Station installation with a 1m wide trench dug underneath to show the shallow track construction and the fact that the track is self supporting over 1 m wide trenches. This was also attended by HMRI ( Kit Holden).

Further in Edinburgh all the utilities were plotted along the proposed tramway and consulted over the use of LR55 tracks. No utility diversions were required but the main gas main at Haymarket would need plating over, as would a 125,000 Volt cable across Leith Walk.

A safe working proceedure was drawn up by HMRI to enable utilities to maintain apparatus while allowing the tramway to continue operation.

2.6.2 Diversion ?

This would be site specific. Only the traffic magnetic loop detectors would be physically obstructed by LR55 tracks and thus need relocation. Inspection pits may need to be moved or modified to fit around LR55 track troughs.

2.6.3 Trench widths ?

The LR55 track has been lab tested over trenches 2m wide and shown to be self supporting. Im is normally wider than most utility trenches and allows for a margin of tolerance during site works.

2.6.4 Routines

Trenches adjacent to tracks would have to be shored like any other trench in the highway. Then there would have to be safe working practice (eg. lookout).

Utilities under a trough ? This would depend on the length. These might be more economically dealt with by digging a parallel trench adjacent to the track and laying a new cable/duct/pipe, unless there is a digless technology eg. removing and replacing the utility in situ.

2.6.5 HMRI Proceedure

See 2.6.1 above.

2.6.6 Temporary Track passing loop

This was invented in 1894 in Liverpool and is widely used on the Continent. It is temporarily installed like model railway track, and sits in the groove with transition rails to a level about 30mm higher than the original tracks. Trams must make this manoevre at slow speed. It would enable one track to be taken temporarily out of use, eg. for replacement as well as utility works.

2.6.7 Powers

These can be included in the Transport & Works Act Order or made by negotiation with the Utilities. Utilities do not usually like to work near other plant, and tramway tracks would be another utility when installed.

2.7 General

2.7.1 Can the rail section comply with standards - BS EN 14811:2006, Is this the relevant standard ?

The LR55 conforms to the German standard relevant to the Ri60 section on which the head and groove profile are based. We are checking with BSI over an equivaqlent BS standard for LR55, which clearly will need to be different from that for girder rails. The Light Rail HMRI David Keay has given very helpful advice on this.

2.7.2 Who rolls this LR55 section - is it commercially available?

To date all LR55 rails have been cast. We are discussing with Corus and a Turkish steel mill , rolling the LR55 section. Mills usually want an initial order of 1000 tonnes to justify the special rolls that need to be cut. GLUAS will need 2000 tonnes of LR55. One of these will provide a commercial offer.

2.7.3 How much?

To date we have worked on the world market price of steel rails, about £650/tonne. We have asked for quotations to supply 2000 tonnes, so will get a much better idea then.

2.7.4 Are Switch and Crossing units available in LR55 or will traditional rail construction still be required in these areas?

Switches and crossing designs with LR55 profiles are available, based on 25m radius and 1:4 crossing angle. The Switch uses a "Tadpole" blade, which can be replaced from above when worn, without having to excavate the track. Special pre cast concrete trough units have also been designed to accommodate the rail switches and crosses. The crosses are also based on a raised grooved for flange running across the rail gap, the so call "silent crossing". The switches are designed to be either trailing (passive but can be worked with a point iron) or facing, power operated remotely from drivers cab, or automatically. In the event of power failure, facing crossings can also be operated by a point iron. Special care will be taken to avoid the recent problems in Poland of hackers changing switches as trams were passing over, leading to derailiments, damage and injuries.

2.7.5 Given the relative lightweight trough support structure - can track gauge be maintained without any gauge ties?

The trough weighs the same as the rail per metre length. The lateral wheel forces of tramcars (or heavy rail) are less than 10% of the vertical forces. The lateral force from one wheel is distributed along the trough side 180mm deep and a length of about 2000mm, at a pressure several orders of magnitude less than the stiffness of flexible pavements. The troughs are very stiff in both vertical and horizontal planes. The rigidity of the pavement keeps the troughs to gauge and so the rails.

Where a flexible pavement is failing, eg. by plastic deformation, and there is no plan to relay, on curves there is a stainless steel strop on which the troughs sit to maintain gauge (every 3000mm). This requires a slot to be cut between rail trenches. The better solution (for everyone) is relaying that length of road and NOT using gauging bars. NB Most tube stations in London have rails not linked by gauge bars or sleepers. For over 100 years the suicide pit has not been a problem for gauge maintnance. Road pavements are equally as stiff as London clay. Finally HGV’s or buses cornering impose much larger (centrifugal) forces on the surface of a flexible pavement. If the pavement can cope with that, it will easily cope with the lower lateral forces of LR55 tracks.

2.7.6 Can vertical loadings from the troughing be supported by the existing sub structure/formation without additional strengthening?

The pressure on the bottom of the trough with 25tonne axles loadings is less than 200MPa. With 10tonne axle loads it is between 50 and 100MPa. The section installed in Rotherham Bus station with 2500 buses per day was laid on asphaltic sand laid on top of a reclaimed rubbish tip. Heavy road vehicles do the most damage to tramway tracks, eg. the shared track in Moseley Street Manchester. The LR55 concrete trough distributes bus and HGV tyre loads into the sub base at a lower pressure, than when they act directly on the pavement surface. All the lab testing up to 80tonne axle loads was on dry conpacted sand.

2.7.7 Can utility repairs really be carried out under tram traffic ? Does the operator want to risk a system closure due to a BWM?

We have a Proposed method of dealing with this from the HMRI. This involves diverting other road traffic off the utility opening, having a look out and trams proceeding on an occupation basis. By and large from the consultations undertaken in the UK, the utilities do not want to move their plant, because:

  1. their design offices are already over loaded on normal supply upgrading
  2. there are always consequential failings at the interfaces (as in US if it ain't bust, don't mend it)
  3. have offered to co-operate in installing ducting as LR55 tracks are laid, so that future repairs or enhancements can be undertaken wihen the utility needs them, without having to dig up the road.

Trenches 1000mm wide can be dug under LR55, which are self supporting for 25tonne axle loads, so no problem for tramways. For a catastrophic utility failure, eg burst gas main, the tramway at that point would be closed whatever track design is used. Thankfully these are 1in 40 year events. The loss of a week’s revenue, once in 40 years is much less than the discounted cash cost of utilitiy diversions over the whole tramway.

2.7.8 Will the larger rail head area give rise to increased skid risk for road users?

The exposed LR55 rail head and PU grout is the same width as eg. Ri59 + grout. For the Sheffield LR55 installation, where there was concern over this, so two different kind of anti skid materials were applied to the non running surfaces of the rail. After over 12 years, these are still good, although worn where most of the road tyres pass.

2.7.9 I am not aware of this system being used on any existing system ?

As above, LR55 track was installed on the Sheffield Supertramway in March 1996, to replace conventional track that had failed after only one year of service. The LR55 has been maintenance free since then, shows little sign of wear, no corrugations or delamination, even though impacted by over 100 40 tonne HGVs per day, and 300 trams on a single track section of the tramway, where a track failure would stop the system.

(c) Lewis Lesley
Feb 2000 - Oct 2008