East London Line Signalling


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East London Line Signalling:

The East London Line (E.L.L.) runs mainly in a cut-and-cover tunnel from Shoreditch to just north of Surrey Quays, from where it runs in the open to New Cross and New Cross Gate.  The line utilises the historic Thames Tunnel at Rotherhide, which was the World's first bored tunnel under a river and was built between 1825 and 1843 originally as a horse and foot tunnel by Marc and Isambard Kingdom Brunel.  The Thames Tunnel was later adapted for use by the Underground.  The E.L.L. is connected to the District Line at Whitechapel by the double-track St Mary's Curve.

Prior to Re-signalling:

Prior to the commencement of E.L.L. Re-signalling Project, the signalling on the line operated thus:

General:

The line (with the exception of New Cross Depot) was fully track circuited.  A track circuit connects the running rails in an electrical circuit to detect the presence of a train on a defined section of track.  Insulated rail block joints defined the sections.

The stop signals were 2-aspect (red/green) equipped with trainstops and additionally 2-aspect (yellow/green) repeating signals provided were installed. There was also 2-aspect (yellow/green) fog repeating signals in sections likely to be affected by poor visibility.  Movements to/from New Cross Depot were controlled by shunt signals.

Whitechapel/Shoreditch:

The District Line cabin at Whitechapel had a miniature lever operated frame and used to house a Westinghouse push-button desk.  The frame controls the signals on the District Line and the moves off the District Line onto St. Mary's Curve.

The push-button desk allowed remote control of Whitechapel E.L.L. Interlocking Machine Room ‘B’ and the subsidiary air-worked power frame on Shoreditch platform individual routes could be act or cancelled, including the route off the E.L.L onto St. Mary's Curve; therefore moves in both directions onto St. Mary's Curve were under the control of the District Line cabin signal operator.

Two auto-working modes could be selected or cancelled, i.e. 'Whitechapel reversing' - whereby the service reversed in Whitechapel platform, and 'Shoreditch reversing’ the service reversed at Shoreditch.  If the control from Whitechapel District Line cabin failed, Whitechapel IMR was designed to revert into 'Whitechapel reversing' auto working mode.

An interlocking machine is an air-operated lever frame incorporating mechanical locking between the levers and electric locks, which allow the levers to be checked at certain positions over their 60 movement.  Electrical contacts detect the positions of the levers and are used in the circuits controlling signals and points.  The levers are operated by air motors, the control of which is classified as 'non-vital', since a failure would, at worst, cause a lever to attempt to move against the mechanical or electric locking.  A handle in fitted to the lever shaft to allow manual operation during testing or failure conditions.

A shaft button route request is converted by lever operation circuitry to produce feeds to the appropriate air motors.  For example, the request to set a route requiring the movement of a set of points would proceed as follows - noting that the point lever must move first and then be locked reverse when the signal lever in reversed to clear the signal:

  1. The momentary operation of the push button energises a route stick relay, which stores the route request.
  2. The circuitry checks that no conflicting routes are obtained.
  3. The circuitry checks that the points are free of mechanical or electrical locking and a feed is then applied to the point lever reverse air motor.
  4. When the circuitry detects that the point lever has reversed, a feed is applied to the signal lever reverse air motor.
  5. As the train passes the signal, the route stick relay is disengaged and a feed is applied to the signal lever normal air motor - sufficient to cause the lever to move off the fully reverse position.
  6. When the train is clear of the point work, the signed lever is fully normalised.
  7. When the circuitry detects that the signed lever is normal, a feed is applied to the point lever normal air motor, to normalise the point lever.

At Shoreditch, a formerly manually-operated power frame, converted for air operation, performed like an interlocking machine.

The emergency release of backlocks was permitted.

An illuminated diagram in Whitechapel District Line cabin showed the position of trains at Whitechapel, Shoreditch and on St. Mary's Curve.

Shadwell to Rotherhithe:

The section of line from Shadwell to Rotherhithe does not include any points and here the signals worked automatically, controlled purely by track circuit occupancy.  The signalling relay and track circuit equipment were housed in location cases within the tunnels.

The Thames tunnel (situated between Wapping and Rotherhithe) had floodgates at the south portal, which were detected 'locked open' in protecting signals.

The position of trains on this section was not displayed on any diagram and therefore there was a gap between the area displayed on the Whitechapel cabin diagram and the Canal Junction cabin diagram.

Surrey Quays Ground Frame:

At Surrey Quays, there was an emergency crossover and trains could make un-signalled reversing moves south-north or north-south.  The crossover was controlled by a six-lever ground frame, four of the six levers being spare.  A ground frame is normally provided to work perhaps just one crossover and is only manned as required.

Lever No. 3 controlled the facing point locks, fitted to both ends of the crossover, and lever No. 4 operated both ends of the crossover.  The ground frame did not directly control the associated signals, but a hand operated screw release was provided to introduce a delay before the facing point lock lever could be operated to withdraw the facing point locks to allow the crossover to be reversed.  As soon as the release started to be operated, all the signals wore placed to danger.  After approximately one minute, the release freed the facing point lock lever, which could then be pulled to unlock the points.  The signals would revert to normal operation after the crossover had been normalised, re-locked and control of the ground frame relinquished.

An illuminated diagram within the ground frame hut showed the position of trains in the immediate vicinity.

Canal Junction Cabin:

Canal Junction cabin was located in the 'Y' of the New Cross and New Cross Gale branches where they diverge at Canal Junction.  The cabin housed a miniature lever power frame controlling Canal Junction, the New Cross branch and the moves to and from New Cross Depot.  The points within the 6-road New Cross Depot, accessed of the New Cross branch, were hand operated by a shunter, who also operated a plunger to accept incoming trains.

The New Crow Gate branch is double track until the convergence at the single platform terminus.  The points operated automatically using circuits originally installed by Railtrack.  Following the arrival of a train at New Cross Gate, the points would be reset for its return trip.

The basic Trains Entering Terminal Station (TETS) protection system was provided at New Cross and New Cross Gate.

Traction current sectionalisation at Canal Junction was such that isolation of either the New Cross or New Cross Gate branches prevented trains running to the other branch.

Following Re-Signalling:

General:

The scope of the East London Line Re-signalling Project did not include the Whitechapel to Shoreditch area, but minor modifications were necessary as described immediately below.

The project provided centralised control of the line from the East London Line signal control facility, situated within New Cross Depot.  A VDU provides an overview or detailed views of the line, showing the position of all trains, including those within New Cross Depot.  Control is at various levels.  Normally routes are set automatically to timetable by the control computer, but the operator has the facility to edit timetable trips; select auto working modes or set and cancel individual routes.  The route off the E.L.L. onto St. Mary's Curve is now controlled by the East London Line signal control facility.

The East London Line signal control facility communicates via a control system with the interlocking at Whitechapel, Surrey Quays and New Gross for controls and indications, and with Shadwell signal equipment room for track section and signal indications.

Track circuits have been converted to jointless type, which require minimal insulated rail joints and offer greater immunity to electrical interference.

The stop signals continue to be 2-aspect (red/green) equipped with trainstops and 2-aspect (yellow/green) repeating signals provided where required.  There are also 2-aspect (yellow/green) fog repeating signals in sections likely to he affected by poor visibility.  Movements to/from New Crow Depot are now controlled by fibre optic shunt signals, which reproduce the displays of the old signals.

Whitechapel to Shoreditch:

The District Line cabin at Whitechapel continues to control the signals on the District line and the move off the District Line onto St. Mary's Curve.  The Westinghouse push button desk, originally used to control signals on the E.L.L., has been removed and the control of these signals and the selection of the two auto working modes has been transferred to the East London Line signal control facility.

If the control from the East London Line signal control facility fails, Whitechapel interlocking machine room reverts to 'Whitechapel reversing' mode, unless 'Shoreditch reversing' is already in operation.

St. Mary's Curve has restricted clearance between the tracks, such that trains cannot be safely passed.  When moves in both directions were under the control of the cabin signal operator, a local signalling instruction covered this special condition.  With the transfer of control of the route from the E.L.L onto St. Mary's Curve the 'slotting' has been added between the cabin and Whitechapel Interlocking machine room, which enforces the working of St. Mary's Curve as a single line.

Whitechapel Interlocking machine room has been retained, together with the lever operation circuitry, but route requests now originate from the East London Line signal control facility via the control system

At Shoreditch, the air operated power frame has been retained.  Trains Entering Terminal Station (TETS) protection has been added at Shoreditch. The speed of a train approaching the terminus is subject to two checks.

Current rail gap indicators have been added to signals at Whitechapel and Shoreditch to indicate to train operators that traction current has been discharged ahead.  Previously the cabin operator, who maintained signals at danger when current was discharged, provided this function.  The emergency release of backlocks is no longer permitted.

The illuminated diagram in Whitechapel District Line cabin has been modified to remove E.L.L. track/section indications, but retains track indications for St. Mary's Curve.

Shadwell to Rotherhithe:

The signalling relays and track circuit equipment for this section of line are now housed within a signal equipment room within Shadwell station.

There is now a transition from conventional and jointless track circuits between Whitechapel and Shadwell.  On the S.B. road, a time delay has been incorporated into signal selections to compensate for the different response times of the two types of track circuit.

The Shadwell, Wapping and Rotherhithe starting signals now feature approach control, and consequently normally display a red aspect, to limit the speed of non-stopping trains and remove the risk of compromise to signal braking distances in the next section.

With the relining of the Thames Tunnel, the floodgates were removed.

Canada Water/Surrey Quays:

A new station has been constructed between Rotherhithe and Surrey Quays, called Canada Water, which will provide an interchange with the Jubilee Line Extension.

The Surrey Quays ground frame has been abolished and relay interlocking provided for the signalling in the Canada Water - Surrey Quays area.

Three modes of auto working are provided: i.e. 'auto through'; 'south to north reversing' and 'north to south reversing'.  If the control from the East London Line signal control facility fails, Surrey Quays relay interlocking reverts to 'auto through' unless another auto working mode is already in operation.  The auto working logic is within the relay interlocking and is therefore independent of the control system.  A local control facility is provided to allow the Station Supervisor to select or cancel auto-working modes.

The design of the relay interlocking allows trains to enter the southbound platform and reverse south to north in the event of a complete failure of the signalling south of Surrey Quays.

The Canada Water and Surrey Quays starting signals now feature approach control to limit the speed of non-stopping trains and remove the risk of compromise to signal braking distances in the next section.

The emergency crossover is retained and is now fully signalled for passenger moves.  Trains can reverse south to north via Surrey Quays southbound platform, and north to south via Canada Water north bound platform or by stopping just north of the crossover.

Route Secure signs have been provided for through moves over the crossover.  These allow a train to proceed at caution if the crossover can be confirmed to be act and locked, but it is not possible to display a green signal aspect, e.g. during a track circuit failure.

Canal Junction - New Cross - New Crow Depot - New Crow Gate:

Canal Junction cabin has been abolished and solid state interlocking provided for the signalling in the Canal Junction - New Cross - New Cross Depot - New Cross Gale area.

The solid state interlocking, has been subject to safety audits and a shadow running trial prior to use on the E.L.L.  The signalling logic, processed every second by the Vital Processor Interlocking, is expressed in the form of Boolean equations.  Relays provide the interface to standard track equipment.

Three modes of auto working are provided: 'alternate New Cross / New Cross Gate reversing'; 'New Cross reversing' and 'New Cross Gate reversing'.  If the control from the East London Line signal control facility fails, the Vital Processor Interlocking reverts to 'New Cross Gate reversing' unless another auto working mode is already in operation.  The auto working logic is within the Vital Processor Interlocking and is therefore independent of the control system.

The points at New Cross Gate have been brought under the control of the Vital Processor Interlocking.

New Cross Depot has been fully signalled, allowance being made for both 4 and 8-car trains on four of the six roads.  The formerly hand operated points have been converted to power operation, but they can become hand workable under failure conditions.

Route-Secure signs have been provided for all signalled moves through Canal Junction.  These allow a train to proceed at caution if the crossover can be confirmed to be act and locked, but it is not possible to display a green signal aspect, e.g. during a track circuit failure.

Traction current sectionalisation at Canal Junction has been modified so that the isolation of either the New Cross or New Cross Gate branch does not prevent trains running to the other branch.

Trains Entering Terminal Station (TETS) protection at New Cross and New Cross Gate has been improved to current standards.  The speed of a train approaching a terminus is subject to three speed checks.