Tramway track
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| Tramway track |
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Tramway track is used on tramways or light rail operations. Grooved rails (or girder rails) are often used in order to make street running feasible. Like standard rail tracks, tram tracks consist of two parallel steel rails.
Tram rails can be placed in several surfaces, such as with standard rails on sleepers like railway tracks, or with grooved rails on concrete sleepers into street surfaces (pavement) for street running. Another environmentally-friendly or ecologically-friendly alternative is to lay tracks into grass turf surfaces; this is known as grassed track (or track in a lawn), first used in Liverpool in 1924.
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[edit] History
The first tramways were laid in 1832 in New York by John Stephenson, to assist horses pulling buses through dirt roads, especially in wet weather when muddy. By laying rails, a horse could easily pull a load of 10 tonnes rather than 1 tonne on a dirt road. The evolution of street tramway tracks paralleled the development from horse power to mechanical, especially electric power. In a dirt road, the rails needed a foundation, usually a mass concrete raft. Highway authorities often made tramway companies pave the rest of the road, usually with granite or similar stone blocks, an extra cost.
The first tramways had a rail projecting above the road surface, or a step set into the road, both of which were apt to catch the narrow tyres of horse drawn carriages. The invention by Alphonse Loubat in 1852 of grooved rail enabled tramways to be laid without causing a nuisance to other road users, except unsuspecting cyclists, who could get their wheels caught in the groove.
[edit] Electrification
Electrification needed other developments, most notably heavier rails to cope with electric tramcars weighing 12 tonnes rather than the 4 tonne horse-drawn variety; switching points, as electric trams could not be pulled onto the right track by horses; and the need for electrical connections, to provide the return path for the electric current, which was usually supplied through an overhead wire.
[edit] Cable haulage
Prior to the universal introduction of electric power, many tramways were cable hauled, with a continuous cable carried in a conduit under the road, and with a slot in the road surface through which the tram could clasp the cable for motion. This system can still be seen in San Francisco in California as well as the system of the Great Orme in Wales. These needed a rather more substantial track formation.
[edit] Conduit and stud systems
In some cities where overhead electric cables were deemed intrusive, underground conduits with electrical conductors were used. Examples of this were New York, Washington DC, Paris, London, Brussels and Budapest. The conduit system of electrical power was very expensive to install and maintain, although Washington did not close until 1962. Attempts were made with alternative systems not needing overhead wires. There were many systems of “surface” contact, where studs were set in the road surface, and energised by a passing tram, either mechanically or magnetically to supply power through a skate carried under the tram. Unfortunately these systems all failed due to the problem of reliability and not always turning off after the tram had passed, resulting in the occasional electrocution of horses and dogs. In the last five years a new system of surface contact has been installed in the Bordeaux tramway by Alstom.
[edit] LR55 system
The grooved girder rail has been the main system of in street tracks, but where new systems or extension are planned the volume of under street utility plant, cables, pipes, ducts and drains means that a concrete raft foundation increases installation costs, since the utilities are inaccessible, and normally need to be relocated. In the years since the first tramway, highway pavement design has progressed around the world. Flexible and rigid pavements are capable of carrying 80 tonne goods vehicles with 15 tonne axle loads at 100 km/h. Using a 19th century tram track system, which destroys a robust pavement and then requires reinstallment, adds costs to tramway track installation and maintenance.
To work with strong highway pavements, the LR55 system was developed, which can be simplified into a “glue” into the road rail. A comprehensive battery of laboratory testing was completed, with up to 80 tonne axle loading, and cyclic testing for 200 million cycles at 25 tonne axle loading.
A test section was installed in Rotherham Bus station in 1993, where some 1 million bus movements a year passed over it. In 30 months it experienced the same heavy road vehicle impacts as 30 years in a typical radial or arterial road. A section of LR55 was installed in the Sheffield Supertramway in March 1996, to replace a section of conventional track that had failed after just one year of operation. This has been maintenance free, shows little sign of wear, and is predicted to last at least 30 years.
Being a mass/spring/mass/spring system, the LR55 offers noise and vibration reduction of some 30 dB. It is also electrically isolated from the ground with a track resistivity of greater than 1000 Ωkm. This means that any stray currents will be in the micro amp range. Finally as a fully sprung track form, the LR55 significantly reduces track corrugations and uneven wear, thereby extending the life of the rails without the need for regular grinding to maintain an acceptable ride quality.
The LR55 track does not need a concrete raft foundation,so under street utilities are still accessible and therefore do not need relocation. The LR55 is also quicker to lay, and can be laid one rail at a time to minimise traffic management problems.
A more detailed discussion of the principles and testing of the LR55 track system can be found on the LR55 [1] website.
[edit] Grooved rail
A grooved rail or girder rail is a special rail designed for tramway or railway track in pavement or grassed surfaces (grassed track or track in a lawn). This was invented in 1852 by Alphonse Loubat, a French inventor who developed improvements in tram and rail equipment, and helped develop tram lines in New York City and Paris.
[edit] See also
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[edit] External links
- ThyssenKrupp handbook (Besides Vignoles rails it shows special grooved girder rail for tramway tracks in pavement)
- LR55 Track System Full details
