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Metrolink Introduction > Track: updated 4 November 2009
There is some 2.5km of street level running within the city centre, much of this is in a reserved right of way; unlike first generation tram tracks that were mostly in the middle of the road.
Underground public utilities; sewers, water and hydraulic pipes, electricity and telephone cables were strengthened or diverted from the route of the track before construction work could begin.
Average foundation depth is approximately 0.5m below former road level. The old roadway surface was broken out and the underlying road construction excavated, including removal of any original tramway rails. After the excavation was bottomed out, a thin layer of blinding concrete was placed to provide a clean working surface.
Steel reinforcing mesh was then placed on top of the blinding and spaced with concrete blocks to provide top and bottom mats of reinforcement. This steel mesh also acts as a conductor drawing off any stray current from Metrolink operation. A structural slab foundation was cast to a level below the foot of the rail. A second slab was added to the first slab to provide two grooves in which to lay the rails. The groove has to be accurately formed to line and level.
Banks of ducts run underground alongside the track slab foundation, within the swept path; they are used for signalling and power cables. Draw pits are positioned every 50m along the track, wherever possible outside the swept path. Various other cables, including those for traffic signals, join the main duct at the draw pits. All operations are then run either automatically or from the Operations Centre at Queens Road.
This used Ri59 grooved rail with a 42 mm groove, it was manufactured in Luxembourg. Each rail was 18m long and weighed approximately 1 tonne. Rails, delivered as straight sections, were bent on site to suit the different radii through the centre. While temporarily supported, the rail lengths were joined using the Thermit welding process.
Once lined and levelled, the rails were embedded in a neat pourable grade polymer which sets to maintain track geometry and provides a resilient support for the track. Permanent steel shutters were then fixed on top of the concrete groove at close tolerances to the rail and the second pour of polymer was installed bulked with sand.
For phase one most of the track on the system is former railway line whose running surface has an inclination of 1 in 20. To match this the rail surface of the street track was lightly ground to increase inclination to 1 in 20 from the 1 in 40 of standard tramway rail.
The Phase One method of securing the rails in place with a flexible polymer is not being repeated.
Road surface and rails were removed down to grooved the base slab. As required the grove edges were cut back to enable a system of fastenings, developed for Manchester, to be set accurately into the concrete.
Pre–coated grooved rail is used with tie–bars between the rails. When the rails are joined together and fastened down a layer of concrete, covering the tie–bars is put in place but leaving space for the road surface layer to go on top.
Sections shared with or crossed by road traffic have concrete beams cast along both sides of the rails, the remaining surface has a tarmac finish.
Other sections, not shared with or crossed by road traffic, have surfaces which include concrete, york stone and cobbles recovered from the original construction.
Track construction for the on street sections used a pre–coated grooved rail. With the rail groove down, in the factory, insulating polymer was applied to almost the full length of each rail. A short length at each end was left uncoated to permit rail joining on site.
The reinforcing steel in the continuous concrete base slab forms the stray current mat. It is connected by cables directly back to the substation. After the concrete base had set, the rail mounting plates were accurately positioned and fixed to the base slab.
The coated rails, bent as required for the differing curves, were placed on the base plates. The fastenings were tightened onto the rail foot holding the rail in place.
With the rails fixed in place the ends were joined by welding or a mechanical joint where welding was not possible. This short length was then polymer coated. Additional reinforcing was positioned before the top concrete layer was laid. This layer did not reach rail top, the final surface being an asphalt layer.
Most of this is former railway line where Metrolink acquired the various types of track that were in use before conversion. Restrictions in available funds prevented the track being upgraded in 1992. By 2007 some of the track was more than 50 years old. In the last few years ride quality had, in some parts, become very poor.
During a major blockade in 2007 all the old jointed track was completely removed and the ground surface prepared before new track was installed. The new track uses twin block sleepers, seen more often in europe than this country, and flat bottom rail. Existing continuously welded rail sections were improved as required.
At track crossings on railway track specially raised check rails are fitted to engage with the backs of Metrolink wheels. These also allow conventional railway wheels, on for example wagons delivering ballast, to pass freely.
These have a modified version of the standard British Railways P8 profile. The tread is inclined at 1 in 20 to match the former railway track on the Altrincham and Bury lines. The flange is thinner than on railway wheels so that it can roll in the 42mm groove of street track. The wheel back is made thicker, at a smaller diameter than the tread, to run clear of grooved rail and engage with the check rails on railway track. This is similar to Karlsruhe in Germany.
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This page was written by Tony Williams, Manchester Area Officer, Light Rail Transit Association. Contact firstname.lastname@example.org if you have any comments, ideas or suggestions about these pages.