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Street Track
There is some 2.5km of street level running within the city centre where Metrolink vehicles run in much the same way as first generation trams did years ago. In fact, excavation for the track in High Street uncovered old tram lines on exactly the same alignment as the new.
Traffic management is the key to Metrolink’s success in the city centre, both during construction and in operation. Manchester City Council dedicated areas of highway on the route to sole use by trams. A judicious adjustment of traffic flows on various streets and highway improvements, maintained the traffic flow after Metrolink had opened.
Before Metrolink construction work could begin underground public utilities:- sewers, water and hydraulic pipes, electricity and telephone cables were strengthened or diverted from the route of the track.
The average foundation depth for the rails is approximately 0.5m below existing road surfacing. The first operation was to break out the existing roadway and excavate the underlying road construction, including removal of any original tramway rails. The excavation was bottomed out and a thin layer of blinding concrete placed to provide a clean working surface. Steel reinforcing mesh is then placed on top of the blinding and spaced with concrete blocks to provide top and bottom mats of reinforcement.
The steel mesh not only provides structural support for the overlying track but also acts as a conductor drawing off stray current induced by movement of the LRVs above. 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.
With completion of the screed laying, work was able to start on the rail laying proper. The rails, manufactured in Luxembourg, are Ri59 grooved rail with a 42 mm groove. Each rail is 18m long and weighs approximately 1 tonne. They were delivered as straight sections and 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 polymer which maintains track geometry and provides a resilient support for the track. The polymer is of a pourable grade. Permanent steel shutters are then fixed on top of the concrete groove at close tolerances to the rail and the second pour of polymer is 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 signalling and power cables for the system run within the swept path, in banks of ducts that run underground alongside the track slab foundation. Draw pits are positioned every 50m along the track and, wherever possible, have been sited outside the swept path.
The various other cables that run include traffic signals joining the main duct at the draw pits. All operations are then run either automatically or from the Operations Centre at Queens Road.
Eccles Line
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.
Segregated Track
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.
Metrolink wheels
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 manwebm@lrta.org if you have any comments, ideas or suggestions about these pages.