Remote Control Overrides

Overview

Remote interlockings operated from the panel box are susceptible to failure if the control link between the panel and the interlocking fails.

In the case of electronic remote controls, an override system is sometimes provided.

Some interlockings are directly controlled and some are controlled by an electronic remote control system.

Electronic Remote Controls

Electronic Remote Controls exist for the following interlockings:

• Uffington
• Bourton
• South Marston
• Chippenham
• Thingley
• Wootton Bassett West
• Hullavington
• Kemble

(Signalling between Highworth Junction and Rushey Platt (inclusive) is "directly and individually" controlled from Swindon by direct wires, so there is no remote control system for these interlocking areas. Wootton Bassett East was controlled by direct wire until ~2010 when a remote control system was fitted. No overrides were provided for this new system.)

The interlocking functions for signalling in these remote control areas is performed in relay rooms at the site, from which the signalling is directly controlled. The controls and indications on the panel for these areas only send requests and receive indications between Swindon and the remote interlocking. (Whereas the controls and indications for the Swindon – Wootton Bassett area work directly to and from the equipment.)

Failure of an Electronic Link

(Rule Book Module T1B, Section 2.3 – Failure of an electronic link)

The failure of the remote control link will be apparent to the signalman by one or more of the following symptoms:

• Signal(s) in the area appearing to not clear;
• Signal(s) in the area appearing to not return to danger after the passage of trains or on turning of the entrance switch to ‘normal’;
• Signal(s) returning to danger of their own accord;
• A whole area of track circuits showing red (#);
• A whole area of track circuits/signals showing black (#);
• A whole area of points out of correspondence (*).

(#) - with or without white lamps flashing through the track circuit / route lamp apertures to denote the limit of the failure.

From the moment the failure of the electronic link occurs, the track circuit, signal and point indications in the area concerned cannot be relied on (T1B, 2.3). So the signalman must disregard all the indications in the area concerned.

In any case, if the signalling becomes inoperable from the normal panel controls, it may be possible to regain a reduced level of control from the Remote Control Override ("Through Routes" and "Selective Overrides").

Panel Indications of Remote Control Boundaries

In the case of remote control failure a single white route light flashes on each line at the boundary of the failure. A single white light is shared between adjacent interlockings and flashes when the remote control either side fails.

The lights are:

Between	And	Line	White lights
Swindon B	Uffington	Down Main	East end (SB)PV End of panel
		Up Main	East end (SB)TB-TE End of panel
Uffington	Bourton	Down Main	West end AM
		Up Main	West end KO
Bourton	South Marston	Down Main	East end AT
		Up Main	East end KG
South Marston	Swindon	Down Main	West end XD
		Up Main	West end YA
South Marston	(Euroterminal)	Goods Reception	West end ZA (End of indications)
Swindon	Wootton Bassett East	Down Main	(See notes)
		Up Main
Wootton Bassett East	Chippenham	Down Main	East end CH
		Up Main	East end HK
Chippenham	Thingley	Down Main	West end CP
		Up Main	East end HE
Thingley	Bathampton	Down Main	West end (B)AC-XG End of panel.
		Up Main	West end GX End of panel
Thingley	Bradford Jn	Single	West end (W)RJ/ETC End of panel.
Wootton Bassett East	Wootton Bassett West	Down Badminton
		Up Badminton
Wootton Bassett West	Hullavington	Down Badminton
		Up Badminton
Hullavington	Chipping Sodbury	Down Badminton	West end DB101-(B)SG End of panel
		Up Badminton	West end UB96 End of panel.
Swindon	Kemble	Single
Kemble	Standish	Down Kemble	West end (G)PT
		Up Kemble	West end (G)PS

Swindon <> Wootton Bassett East - Wootton Bassett East used to be direct wired, but latterly was controlled by Remote Control. Not sure if indication lamps were fitted at the boundary....

Remote Control Overrides

Obtaining Overrides

Through routes is selected by turning the 'SIGNALS RED / NORMAL / THROUGH ROUTES' switch to the 'THROUGH ROUTES' position. Turning the switch away from 'NORMAL' will place all the controlled signals and auto signals with emergency replacements in the area to danger.

The lamp above the switch will flash white for a period of time to effect approach locking and make sure everything is at a stand (a train could have been travelling through the area at 125mph at the time of the failure). At the expiry of this time the lamp will turn steady white, and the 'ROUTES FREE' lamp will show up steady white. Also at this time any controlled signals that don't protect any points and any auto signals with emergency replacements will be cleared and will act as auto signals for the duration of the use of the override.

Selecting an Override

Provided that the 'ROUTES FREE' lamp is illuminated it is now time to choose either the THROUGH ROUTES or a SELECTIVE ROUTE. There are a limited number of routes available for each interlocking area to enable trains to keep moving, but without full flexibility of junction moves or reversible working. The various overrides are identified by the routes involved which are written above the relevant button, ie, '20A 83A' for up and down the Mains at Bourton. The signalman must press AND HOLD IN the button for the Through Route or Selective Route required. Hold it in while the 'ROUTES FREE' lamp extinguishes, the selected override lamp flashes white while the route is being set up and then finally comes on STEADY when the routes are finally set. When the lamp comes on steady the button can be released. The required override has now been obtained.

The illumination of the Through or Selective Route lamp is the signalman's PROOF that the request for the through route or selective route has been registered and obtained and the points are lying correctly. It does not mean the signals have cleared, they are still subject to the normal track circuit and approach release controls as appropriate. The points may well be flashing on the panel and the track circuits may well be showing occupied, but remember that the interlocking functions are being carried out in the relay room at the site – it is (or may be) only the link to and from the panel buttons that has broken. The Through or Selective Route lamp being illuminated is the signalman's assurance that if the signals on the ground clear, the points are lying correctly. If the points were to lose detection the signal interlocking will be maintained.

Emergency During Overrides

If, during the use of the overrides it is necessary to place a signal to danger in an emergency, the operation of the panel switches will be ineffective (as they are being overridden). Instead, the 'THROUGH ROUTES' switch must be turned to the 'SIGNALS RED' position. This will cancel through routes and place all controlled and auto signals with emergency replacements encompassed in the through routes to danger. Approach locking will be effective where appropriate.

'Through Routes' and 'Selective Routes'

In the case of THROUGH Routes (not selective routes) the signals concerned will work as automatics and will step up normally after the passage of each train. These are normally the 'straight up and down' selections. Trains can follow each other through the section, they will 'disappear' from the panel indicatoins when they enter the failed section and 'reappear' at the other end. (See the note about train descriptions below.) There is no limit on the number of trains that can follow each other through the section (apart from the number of signal sections available) and normal TCB rules apply throughout.

In the case of SELECTIVE Routes (not through routes), the signals concerned will return to danger when the train passes them and then stay at danger. These are normally the 'reversible' selections and the 'one on' or 'one off the branch' selections. In these cases it can be seen when the train has passed the signal by the Selective Override lamp being extinguished. The 'ROUTES FREE' lamp will not illuminate at this stage, as that will not do so until the train concerned has gone all the way clear of all the points etc (and hence the route is free to be changed or reused).

Behaviour of Train Describer

If the Remote Control Override is being used due to signals returning to danger of their own accord (ie, the link is ‘blipping’), it may be the case that the indications in the panel are still largely working. In this case, it is helpful to set up the routes on the panel in sympathy with your Selection on the Remote Control Override. This will have NO effect on the signalling outside equipment whatsoever (remember, we are overriding the remote control), but it will allow the train describer in the panel to work correctly. The TD is a non-safety critical system, and as such it steps the descriptions based on the track circuit indications, which is gets through the remote control, however it will only do this if the remote control system 'thinks' the signals are cleared. The TD can't recognise signals being cleared by override, only by the panel controls, so operation of the panel switches will fool the describer into believing that the remote control is working and it will then step the descriptions (99% of the time). If the nature of the failure is such that the panel indications are completely extinguished for the area concerned then the TD has no way of 'seeing' even TC indications, so the signalman must make a note of the descriptions as they enter the 'black hole’ and re-interpose them when they come out the other end (describing by telephone to an adjacent box if necessary).

Changing the Route

If, having selected a through route, it is necessary to cancel it and select a new through or selective route, the 'CANCEL' button should be pressed until the 'ROUTES FREE' lamp illuminates and then a new route can be selected.

Resuming Normal Working

Through Routes may only be cancelled with the permission of the technician.

IN THEORY it should be possible to set up the routes required on the panel in sympathy with the override selected, and if a green light is shown above the 'SIGNALS RED / NORMAL / THROUGH ROUTES' switch then that switch can be returned to the 'NORMAL' position and normal working resumed immediately without any changes of aspect on the ground. This works (in theory) because the override and the remote control (which is now working) are set for the same routes, so changing from one system to the other has no effect outside.

HOWEVER, wiser signalmen might like to wait until there are no trains in the area and then use the 'CANCEL' button to cancel the currently selected route until the 'ROUTES FREE' lamp illuminates and then, if a green light is shown above the 'SIGNALS RED / NORMAL / THROUGH ROUTES' switch then that switch can be returned to the 'NORMAL' position and normal working resumed. That way there is no danger of a COA.

See special note about Thingley / Chippenham resuming normal working.

Specialities and Quirks

Uffington

THROUGH routes provided for:

• Up and down the Main.

SELECTIVE routes provided for:

• Down movements Up Main Reversible to Down Main;
• Up movements Down Main Reversible to Up Main.

Bourton

THROUGH routes provided for:

• Up and down the Main.

SELECTIVE routes provided for:

• Down movements Up Main Reversible to Down Main;
• Up movements Down Main Reversible to Up Main.

South Marston

There is no override at South Marston, instead TWO remote control links are provided: 'STSYEM 1' and 'SYSTEM 2'. Switches are provided on the panel above the South Marston tiles to control the links and alarms. The fault bell will ring if either link fails and the lamp will flash to indicate which alarm. The links should automatically change over if one fails. The alarm is silenced by turning the switch. If BOTH links fail, game over.

Thingley & Chippenham

THROUGH routes provided for:

• Up and down the Main.

SELECTIVE routes provided for:

• Down movements Up Main Reversible to Down Main;
• Up movements Down Main Reversible to Up Main;
• Up Branch to Down Main Bi-directional;
• Down Main to Down Branch

NOTES:

• There is one Remote Control Override for the Thingley and Chippenham interlocking areas with lots of routes. Not all routes are provided with overrides, but some can be achieved in stages. For example, a train off the branch onto the Up Main can travel from SN.11 to SN.627 in selective override, then when the 'ROUTES FREE' lamp illuminates the SN.627 to SN.29 selective override can be used. (SN.29 will be working as an auto throughout, see above.)
• If a train requires to access the Down Branch, selection of the selective override for that route will hold the Up Main signals at danger. Clearance of the Up Main signals is only achieved by selecting the Through Route that also clears the Down Main signals (for the 'wrong' route towards Bathampton). The last controllable signal on the Down Main is SN.62 at Wootton Bassett East Junction, at which signal the branch train would, in theory, have to be held until the Down Branch override was selected, which would cause extensive delays on the Up Main while the branch train travelled from Wootton Bassett to Thingley Jn. The best-practice solution to the problem is to select the 'Up and Down the Main' override. The driver of the branch train can be instructed at Swindon (or wherever) that the signals will be cleared down the Main at Thingley, and to stop at SN.74 regardless of the aspect displayed. When the driver does this, and a suitable margin on the Up Main exists to legally replace those signals to danger, the 'CANCEL' button can be pressed to cancel the routes up and down the main, then, after the timeout, and 'ROUTES FREE' lamp illuminated, the selective route onto the Down Branch selected. Not brilliant but the best solution in bad circumstances.
• IMPORTANT NOTE – When resuming normal working at Chippenham & Thingley, it is important to select the through routes for up and down the main, then to set up the sympathetic routes on the panel, then turn the 'SIGNALS RED / NORMAL / THROUGH ROUTES' switch back to 'NORMAL'. Resuming normal working without the sympathetic routes set up and down the main at Chippenham & Thingley will cause the system to malfunction.

Wootton Bassett West

THROUGH routes provided for:

• Up and down the Badminton.

SELECTIVE routes provided for:

• Down movements Up Badminton Reversible to Down Badminton;
• Up movements Down Badminton Reversible to Up Badminton.

Hullavington

THROUGH routes provided for:

• Up and down the Badminton.

SELECTIVE routes provided for:

• Down movements Up Badminton Reversible to Down Badminton;
• Up movements Down Badminton Reversible to Up Badminton.

NOTES

• Before operating the 'SIGNALS RED / NORMAL / THROUGH ROUTES' switch to the 'THROUGH ROUTES' position, place all the individual points switches for the area concerned into the CENTRE position. Otherwise through routes cannot be obtained. Reason unknown.
• No routes provided into or out of the loops.

Kemble

• There is no override at Kemble, instead TWO remote control links are provided: 'SYSTEM A' and 'SYSTEM B'. A 'REMOTE CONTROL RESET' button is provided on the panel to control the links. A siren will sound if either link fails, accompanies by a 'SEMI-URGENT ALARM' lamp flashing. The links should automatically change over if one fails. The alarm is silenced by pressing the 'REMOTE CONTROL RESET' button. If BOTH links fail, the siren will sound, an 'URGENT ALARM' lamp will flash, Kemble will go black, game over.
• Note that as there is no UPS at Kemble, the failure of the power supply will cause a signalling blackout which will initially manifest itself as a complete failure of both links. If/when the power or generator comes on the signalling will come back to life and just the power indication will show up.
• Also at Kemble, a 'PANEL INDICATIONS' button is provided. For up to five minutes after a signalling blackout has occurred, operation of this button will cause the panel indications to show a 'snapshot' of the state-of-play immediately before the failure, ie position of trains, etc. Note, this may not be the current situation any longer.

Occasions when Overrides are not allowed

The operation of remote control overrides will cause the panel buttons to lose control of the interlocking and hence the signals and points (if they haven’t already), this includes all controlled signal switches and emergency replacements. If, for any reason, it is necessary to maintain any signals in the area at danger then Through Routes must NOT be selected until the signalling technician has DISCONNECTED the signal(s) concerned. This is the only way to maintain single signals at danger during use of Remote Control Overrides.

This might be due to single line working, T2/T3/T12, 3.5 working, cautioning, protecting a non-guaranteed machine, etc. In which cases trains will require to be talked past at danger (but remember you’ll need some way of knowing that the train has passed that signal section complete because the panel indications cannot be relied on – ie, tail lamp man or 2-1 from adjacent box).

Through Routes may not be used during a track circuit failure.

Through Routes may not be used if a wrong direction movement is taking or requires to take place.

There are no overrides for signalling trains into a reversible section (but there are for signalling them out). So if reversible working is in operation, the overrides can only be used in the right direction.

[Danny Scroggins, Swindon B, March 2008.]