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Tram Management System (TMS)

Metrolink opened in 1992; it was first modern light rail system in England combining segregated running on the former Altrincham and Bury heavy rail lines and street running in Manchester city centre. Two aspect track circuit block signalling; like that on the Tyne and Wear Metro; was provided on Altrincham and Bury lines. Street running in the city centre was line–of–sight. See the Signalling page for more details.

English light rail systems which opened after Metrolink had line–of–sight operation throughout from day one.

Metrolink’s Phase 3 extensions almost tripled the network size. It was felt that a block signalling system would not be able to support the desired headway between trams (zero minutes) and level of flexibility required. Transport for Greater Manchester (TfGM) decided to have line–of–sight operation throughout.

Drive on sight

This has been implemented from the start on Phase 3 lines; the city centre and Eccles lines have been converted. Roll-out is proceeding outwards, in stages, towards Bury and Altrincham.

On segregated lines the maximum speed is 50mph. Where sighting distance is limited, a reduced maximum speed ensures that drivers can stop within sighting distance.

For the Collyhurst and Heaton Park tunnels where sight lines are compromised by line gradient and curvature; an innovative solution is used. Axle counter sections detect the presence of a tram in the tunnel and switch a variable speed sign to display a lower speed limit for a following tram.

TMS line–of–sight is different from the previous line–of–sight in the city centre. It gives Metrolink Control a more precise position for each tram and enables the new Passenger Information Displays to show accurate information.

Route setting

With TMS there are no continuous track circuits, to locate trams, or centralised route setting and interlocking system.

Journey information, derived from the timetable, is downloaded to the trams; enabling the tram to automatically route itself at junctions. At junctions where routes diverge and join, they are set on a first–come–first-served basis.

In the event of an incident, which could have network wide consequences, controllers may need to intervene and change the timetable and/or individual tram schedules to minimise delays and aid service recovery.

Route setting requests are automatically transmitted by a transponder on the underside of the tram to inductive detector loops in the space between running rails, known as the four foot. When the junction becomes available, the tram gets a proceed indication.

Signals, with white lights, are normally at stop and change to proceed as the driver approaches. Separate points indicators are sited at the toe of facing points; they confirms detection of ‘points left’ or ‘points right’ and are independent of the signals. Points indicators have orange lights to distinguish them from signals.

Tram Location and Tracking

Metrolink uses the VECOM system; this has fixed loops at key locations which pick up route and other data from the tram. Additionally at certain locations, the tram sends location data determined by the odometer (wheel rotation counter) over the internal mesh radio network. At tram stops, the VECOM loop’s known exact position, enables tram location to be precisely updated.

Two VECOM transponders are mounted underneath the car body (one for each half). They cannot be in the same place as the older VRS coils on the un–motored centre bogie. The active transponder is under the leading half of the tram.

The Mesh Radio Antenna is mounted on the vehicle roof. Corresponding Mesh Radio Access Points are mounted on overhead line equipment poles.

Signal and Point Control

Relies on programmable logic controllers (PLCs) for control of discrete geographical zones, which are usually based on tram stops or significant junctions. Each zone is designed to communicate back to the Control Centre via the Metrolink fibre optic backbone network. However each zone must be able to continue to operate autonomously should communications be lost. Signals in off street areas are controlled by PLCs using inputs from the tram detection equipment. For on street signals; the tram detection system sends a request to the highway Traffic Signal Controller, which controls traffic lights and tram signals.

Points are controlled by independent points controllers using tram detection system data initially processed by the PLC. The points controllers possess a high degree of safety.

Additional detection systems

These are provided for points, to prevent them moving under a tram. Off street location usually use axle counters. For on street locations mass detector/track circuit combinations are used.

Signal Passed at Stop (SPS) detection may use axle counters or mass detectors to drive the blue flashing beacons. SPS beacons are used on single line sections and at junctions where there is not a clear line of sight for trams that may make a conflicting move.

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This page was written by Tony Williams. Contact if you have any comments, ideas or suggestions about these pages.