|Light Rail Transit Association
Light Rail for better public transport
Metrolink Introduction > T68 & T68a: updated 28 July 2014
In the original Metrolink six line plan; five rail lines would have been converted, the Didsbury line re–built and the short City Centre sections built. At the time low floor car technology was in its early stages; so it was decided to use double ended high floor cars which matched British main line platforms.
The Firema Consortium provided twenty–six T68 trams, numbered 1001 to 1026 for the Altrincham, Bury and city centre (phase 1) lines. Originally these could only run between Altrincham and Bury, direct or via Piccadilly.
The profiled platforms were designed for city centre stops at High Street, Market Street, Mosley Street and St. Peter’s Square where space was relatively limited. They have all been replaced or removed. For a single tram at these stops, the centre doors — those on each side of the articulation, had level access. There was a slight step down from the other doors.
Four 1.22m wide doorways were provided each side, with externally–hung double sliding door leaves. Drivers released the doors at stops, which were opened by passenger–operated push buttons mounted at each doorway. On the second of two units, a retractable step about 700mm above rail level, operated automatically with the doors. These enabled passengers to step down to the lower part of the profiled platform.
The Ansaldo Breda Consortium provided six T68a trams, numbered 2001 to 2006, for the Eccles (phase 2) line. From 1999 till 2009 they were only allowed to run between Eccles and Piccadilly or Victoria and Queens Road Depot.
T68a trams also had Four 1.22m wide doorways on both sides. These were only worked as single units, not using their steps at profiled platforms.
For the Eccles line opening, numbers 1005, 1010 and 1015 were modified and able to operate throughout the network.
All the T68 and T68a units were to be modified for universal running. Further alterations to make them fully DDA and RVAR compliant were also required.
The old trams have proved to be less reliable than the new M5000 trams. In September 2011 it was decided to accelerate replacement of T68 trams. 12 more M5000s were ordered. In June & July 2012 GMCA and TfGMC agreed to replace the rest. An order for a further 20 new M5000s was placed in July. All 32 of the T68 and T68a vehicles have been withdrawn from service.
|Facts & Figures|
|Track Gauge||1.435 metre|
|Length of Tram||29.84m over fixed couplers, T68|
29m over body, modified T68
29m over body T68a
|Width of Tram||2.57m over body shell|
2.65m at door sills
|Entrance and Floor height||915mm above rail level throughout|
|Wheel diameter||740mm (new)|
|Height of Tram|| 3.36m over body|
3.7m over retracted pantograph
|Weight||49 tonnes empty|
|Nominal platform gap||75mm for phase one|
40 mm for phase two
|Seating capacity||82 plus 4 pull down seats|
|Standing||122 at 4 per square metre|
|Nominal loading capacity||200 with a crush–load of 250|
|Maximum speed (off-highway)||80km/h (50mph)|
|Maximum speed (street running)||48km/h (30mph)|
|Minimum curve radius||25m|
A welded steel construction was used for the vehicle bodies. The floor consisted of composite wood sheets mounted on stainless steel with an abrasion–resistant rubber covering. Laminated materials lined the saloon walls, these were moulded to form window recesses. Light alloy panels lined the ceiling, there were two rows of semi–recessed fluorescent light fittings and central air distribution ducts. At floor level along the side walls thermostatically–controlled heaters were provided. The main saloon windows included a hopper–type opening section at the top of the window. Sealed windows were provided next to the articulation and in the doors.
The driver’s cab had a deep windscreen and long side windows for all around vision. Self–retracting mirrors, on each side of the cab, allowed the driver to see the length of the tram when at a stop. For phase 3 these were replaced by rear view CCTV. Vehicle ends were tapered, for almost the length of the cab, to provide clearance for vehicles passing on 25m curves. The driver’s position was on the cab centre line with a wrap–around console carrying the various controls (radio, public–address, heating, ventilation, lighting etc).
Two areas (adjacent to the centre doors) were specially set aside for wheelchairs and a further two areas were allocated for parcels/luggage. Fold down seats provided there could be used by other passengers if the spaces were not required for their prime purpose. The articulation gangway was wide enough to allow wheelchairs to move freely from one section to the other.
Floor height relative to the platform was maintained nominally constant by the air suspension system. Drivers had to close all open doors before the tram could depart.
A three position control selected running modes, segregated, street running or street running with steps. The with steps mode was for street running where there were the profiled platforms.
Each tram had three bogies, the two outer bogies were powered. The unpowered centre bogie supported the articulation gangway. Under full–load conditions almost 70% of the weight was on the powered bogies, which assisted the hill–climbing ability of the trams. The powered bogies each had two 105kW motors, separately–excited dc on phase 1 and three–phase ac on phase 2.
Each pair of dc motors was fed from independently controlled choppers utilising gate turn off (GTO) thyristors. The separate field control was provided by 4 quadrant inverters with insulated gate bipolar transistor (IGBT) technology. The choppers were microprocessor controlled operating at an interlaced chopping frequency of 600 Hz. A frequency monitoring circuit prevented chopper frequency deviating into signalling frequencies.
The three–phase ac motors were lighter, more reliable, require less maintenance and were more cost effective. They use IGBTs in the power control circuits, thus minimising the power electronic components and allow cooling techniques that insulate the high voltage electric components from dust and moisture.
Another 4–quadrant IGBT inverter was the ac source for the transformer/rectifier which produces the 110V dc supply used for battery charging, also providing control and auxiliary supplies.
The line filter performed three functions: it presented a low impedance source to the chopper; it presented a high impedance to the ac voltage component in the overhead 750V supply and it filtered out chopper–generated ripple.
A programmable logic controller was used to reduce the number of control relays, thus providing space savings and giving greater flexibility of operation.
The driver’s left hand was used to operate a joystick–type controller for acceleration and braking. This had a “T” shaped handle which, when released, was sprung to return back to the full emergency brake position with its top bar in a fore/aft alignment.
The TBC was made active by a key–operated switch. To move, the driver turned the TBC handle clockwise to a left/right alignment and moved it forward past the midway “Coast” position applying power. At the required speed the TBC was held in the “Coast” position. To brake the TBC was drawn back from the midway position. If the TBC was allowed back past the slight detent which marks normal service braking, the emergency brake was applied; this was the driver’s safety device. A thumb operated button on the TBC sounded the horn.
The braking system was fully–blended, using regenerative/rheostatic electric brakes on the motored bogies and pneumatic brakes on all bogies. Energy which the line cannot absorb was dissipated from naturally–cooled resistors mounted on the roof of the tram. Electric track–brakes fitted to all bogies provided a significant additional braking force under emergency conditions, allowing the tram to operate safely with normal road traffic. Emergency braking is applied by pulling the Traction Brake Controller one notch beyond the service brake position. On phase 2 units, and modified phase 1 units, the emergency brake system consists of both air brakes and the electromagnetic track brakes. It can be released and reapplied as required.
Unmodified phase 1 tram couplers were fixed, phase 2 and modified phase 1 tram couplers were retractable. Extension and retraction — using a scissors’ mechanism — was pneumatically operated. It was controlled by push button in the cab and included a locking mechanism in both the extended and retracted positions. Manual operation of the auto coupler was possible by use of a steel bar housed on the scissors arm. The coupler head consisted of the mechanical connection, a pneumatic air line valve and an electrical head containing 130 contacts protected by a retractable cover. Retracted couplers were covered by front fairings.
On the phase 2 and modified phase 1 trams all three bogies were fully covered with protective side panels/skirts. This and the retractable auto couplers were required as the Eccles route is almost entirely at street level and beyond Broadway will shwere the carriageway with other road users
From the start phase 2 trams had their external doors coloured contrasted — both inside and out — to make them more visible. Note that after mid–life refurbishment, the phase 1 tram doors were also colour contrasted on the outside.
T68 & T68a: top of page
This page was written by Tony Williams, Manchester werea Officer, Light Rail Transit Association. Contact firstname.lastname@example.org if you have any comments, ideas or suggestions about these pages.