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Signalling for Light Rail

Light Rail vehicles have much shorter breaking distances than main line trains. Signalling requirements depend on the operating conditions and layout.

By the 1970s in England there was only the Blackpool System in operation; this is driven on sight and has both segregated, the promenade, and shared with traffic street running.

In 1980 the Tyne & Wear Metro opened. Centred on Newcastle–upon–Tyne, it took over run–down urban railways and linked them with new tunnels under Newcastle and Gateshead also a new bridge across the Tyne. Entirely segregated and electrified at 1500 V dc it is manually driven.

The Tyne & Wear Metro has 2–aspect red/green signals with track circuit block operation. Distant signals, in the main–line sense are not required. If obstructions restrict signal sighting, yellow/green repeaters may be provided.

Docklands Light Rail, London, opened in 1987. This is an entirely segregated, automated system with under–running third–rail at 750 V dc traction supply.

Metrolink: Altrincham, Bury, City Centre and Eccles lines

Metrolink opened in 1992 with a railway like fixed block two aspect signalling on the segregated Altrincham and Bury lines. Line of Sight working was provided in the city centre. In 1999 Line of Sight working was also provided from Pomona to Eccles.

The following sections describe Phases 1 & 2 arrangements

Vehicle Recognition System (VRS)

This was used to send information from the vehicle to both Metrolink Control and the street running signal system. The VRS equipment generated a modulated carrier signal which was transmitted by a pair of coils, mounted one after the other under the un–motored centre bogie. The VRS signal was picked up by cable loop, buried in the road surface or mounted on the sleepers of segregated track.

At the start of each journey the driver entered a route code into the VRS control panel. That set up the description of the tram on the diagram at Metrolink control; it also, where required, called for the points to change on street running sections. The “ready to start” request was also sent by the VRS.

Segregated sections

Heavy rail sections were totally resignalled. Formerly the Altrincham line had four aspect colour light signals and track circuit block (TCB) working; the Bury line had both colour light signals with TCB and semaphore signals with absolute block working.

Metrolink TCB working had two aspect (red/green) signals, mostly sited at station platform ends. Additional signal sections were provided where traffic levels justified it, such as between Cornbrook and G–Mex. Repeating yellow/green signals were only provided where there was a restricted view of stop signals. Signals and points were interlocked at junctions using solid state interlocking (SSI). Relays were used to control plain line signal sequences.

Light rail vehicle braking distance is so short that main line railway style distant signals were not required. Automatic Tram Stops (ATS) were provided at stop signals. If a vehicle passed a stop signal at red, even under instruction from control, the ATS caused an emergency brake application using the electromagnetic track brakes. Even at very slow speed this was so sudden a deceleration that drivers announced the event warning passengers to brace themselves.

Metrolink controls all the segregated section signalling except that from just south of Timperley to Altrincham inclusive. Here trams run alongside main line trains and over two level crossings under Network Rail control.

Street running

In street running areas where trams are driven on sight; a new form of signal head was devised. This consisted of a cluster of white lights, lit according to the indication required. Each aspect lit five lamps; failure of any two would not obscure the display’s meaning. A horizontal line indicates “stop”, a vertical line “proceed” if the road is clear of obstruction, a diagonal line “proceed to left or right” and a “+” sign cluster “stop if it is safe to do so”.

As the tram passed over detection loops buried in the road, the VRS requested a tram “proceed” indication from the road traffic signal Urban Traffic Control System.

When ready to depart from a stop and cross a road the “ready to start” request was also sent by the VRS.

Facing points at junctions were called to change position, if required, by a signal from the VRS. The control circuits only allowed point movement when the tram driver could see them move, they also prevented movement when a tram was moving over the points.

Street running signals were not interlocked with facing points at junctions. A separate seven light fibre optic indicator was used to show that the points were set and locked. The indication was a diagonal line of white lights indicating left or right route. If the points are not detected as set in the direction called then the point indicator shows a horizontal white line for stop.

Facing junctions on the system were a choice of one route from two. Both point indicator and tram traffic signal showed a matching diagonal indication.

Phase 3

For Phase 3 extensions, a new Tram Management System (TMS) has been provided. This is based on Line of Sight working, however, it is different from the previous line of sight working which is described above.

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