Lineside Signal Aspect Sequences

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1 ailway roup Standard K/T0032 Lineside Signal Aspect Sequences Synopsis This standard defines the sequence in which lineside signal aspects shall be presented to train drivers. This document is the property of ailtrack PLC. It shall not be reproduced in whole or in part without the written permission of the Controller, Safety Standards. Published by Safety & Standards Directorate ailtrack PLC Floor 2, Fitzroy House 355 Euston oad London NW1 3A Copyright 1995 ailtrack PLC

2 ailway roup Standard K/T0032 Page 2 of 13 Withdrawn Document Lineside Signal Aspect Sequences This page is intentionally blank. 2 A I L T A C K

3 ailway roup Standard K/T0032 Lineside Signal Aspect Sequences Page 3 of 13 Contents Section Description Page Part A Issue record 2 esponsibilities and distribution 2 Compliance 2 Health and Safety esponsibilities 2 Supply 2 Part B 1 Purpose 3 2 Scope 3 3 Definitions 3 4 Introduction Consistency of Signalling 4 5 Colour Light Aspects Aspect Sequences Leading to a Stop Aspect Aspect Sequences for Advance Warning of Diverging oute Approach Control of Aspects Segregation of Three and Four Aspect Signalling Semaphore Equivalent Aspect Sequence 7 6 Semaphore Aspects Aspect Sequence Leading to a Stop Aspect Aspect Sequence for Advance Warning of Diverging oute 7 7 Prohibited Aspect Sequences 7 8 Miscellaneous Aspects and Indications Stop Board Points Indicator Buffer Stop emote round Frame Marker Board 8 eferences 9 Appendices A Illustration of Transition from 3 to 4 Aspect Signalling 10 A I L T A C K 3

4 ailway roup Standard K/T0032 Page 4 of 13 Withdrawn Document Lineside Signal Aspect Sequences Part A Issue record This standard will be updated when necessary by distribution of a complete replacement. Amended or additional parts of revised pages will be marked by a vertical black line in the adjacent margin. Issue Date Comments 1 October 1995 New Standard. Supersedes SSP22, SSP23, and SSP66. esponsibilities and distribution Compliance Health and Safety esponsibilities Supply Controlled copies of this standard shall be complied with by all personnel who are responsible for the design of lineside signalling systems. The provisions of this ailway roup Standard are mandatory and compliance is required for new or altered works from 3rd February etrospective action is not required. In authorising this Standard ailtrack PLC makes no warranties, express or implied, that compliance with all or any of ailway roup Standards is sufficient on its own to ensure safe systems of work or operation. Each user is reminded of its own responsibilities to ensure health and safety at work and its individual duties under health and safety legislation. Controlled and uncontrolled copies of this standard must be obtained from The Catalogue Secretary, ailtrack Safety & Standards Directorate, Floor 2, Fitzroy House, 355 Euston oad, London, NW1 3A. Telephone: Facsimile: or (BT) or (BT) 4 A I L T A C K

5 ailway roup Standard K/T0032 Lineside Signal Aspect Sequences Page 5 of 13 1 Purpose 2 Scope 3 Definitions Part B To define the sequences in which lineside signal aspects shall be presented to the driver to ensure that the information conveyed is consistent and unambiguous. Permissible sequences of all main signal aspects defined in K/T0031 (Lineside Signals and Indicators) are defined in this standard. Only systems of signalling which employ cautionary aspects are considered. oute Indications, banner repeating aspects, position light aspects, semaphore subsidiary and shunt aspects, do not lie within the scope of this standard. Aspect Sequence: The order in which the aspects of successive signals are displayed to the driver. Standard Three Aspect Sequence: The following colour light aspect sequence is referred to as a standard three aspect sequence: reen ellow ed Standard Four Aspect Sequence: The following colour light aspect sequence is referred to as a standard four aspect sequence: reen Double ellow ellow ed Minimum Signal Spacing Distance: This is the minimum distance (as defined in K/T 0034) between the first cautionary aspect and the stop signal (or equivalent) to which that cautionary aspect applies. Continuous Sequence of Signals: 4 Introduction A sequence of colour light signals in which each stop signal is also capable of displaying a caution aspect relating to the succeeding signal. The aspects defined in K/T0031 (Lineside Signals and Indicators) shall only be displayed at successive signals in sequences which convey logical and consistent instructions to the driver. All signalling shall be designed to ensure that the driver receives sufficient forewarning of the need to stop, bearing in mind signal spacing (as determined by K/T0034 Lineside Signal Spacing) and train performance. At junction signals, a clear and unambiguous route indication shall be provided. Where a previous signal also conveys an indication of the route to be taken at the junction, the driver shall be given equivalent route information at any intervening signals. A I L T A C K 5

6 ailway roup Standard K/T0032 Page 6 of 13 Withdrawn Document Lineside Signal Aspect Sequences 4.1 Consistency of Signalling Signalling shall be designed with the aims of assisting the driver in the following respects: to correctly understand the sequence of aspects leading to a stop aspect; to regulate train speed to safely negotiate junctions; to regulate train speed to match that of an immediately preceding train. 5 Colour Light Aspects These aims shall be furthered by avoiding intermixing of sequences which utilise the preliminary caution aspect and those which do not. 5.1 Aspect Sequences Leading to a Stop Aspect Three Aspect Signalling A driver, running under authority of a green aspect in a three aspect section of line, shall be forewarned of a stop aspect by the standard three aspect sequence (the only permitted exceptions to this principle are as described in this Clause 5.1.1). The yellow and red aspects shall be separated by at least minimum signal spacing distance. Where it is necessary to position signals such that the required spacing between a yellow and a red aspect in the standard three aspect sequence cannot be provided, sufficient warning of the stop aspect shall normally be provided by means of an isolated standard four aspect sequence (subject to the constraints of Paragraph 5.4). Where it is necessary in such cases to employ approach control (in order to meet the requirement of K/T 0034 for spacing between the yellow and the red aspect in a four aspect sequence), the standard four aspect sequence shall be displayed on the approach to the approach controlled signal Four Aspect Signalling A driver, running under authority of a green aspect in a four aspect section of line, shall be forewarned of a stop aspect by the standard four aspect sequence (the only permitted exceptions to this principle are as described in this Clause 5.1.2). The double yellow and red aspects shall be separated by at least minimum signal spacing distance. Where it is necessary to position signals such that the required spacing cannot be provided between a double yellow and a red aspect in the standard four aspect sequence, the double yellow aspect shall be additionally displayed at sufficient preceding signals such that minimum signal spacing distance is provided between the outermost double yellow aspect and the red aspect. Such sequences shall be avoided unless absolutely essential. Where it is necessary to position signals such that the spacing between the yellow and the red aspect does not meet the requirements of K/T 0034 for a four aspect sequence, the signal immediately prior to the signal at danger may be approach controlled. In such cases, the yellow to red spacing requirement of K/T 0034 shall be taken to apply to the signal whose danger aspect was first considered, rather than the signal which is approach controlled for this purpose. It is, however, essential that a double yellow aspect is displayed at minimum signal spacing distance from the approach controlled signal. 6 A I L T A C K

7 ailway roup Standard K/T0032 Lineside Signal Aspect Sequences Page 7 of Where No Main oute eads up to a Signal (eg. Starting from Terminal Platforms) A signal which cannot be approached under authority of a main aspect (known as the starting signal in the context of this Clause 5.1.3) may show a red aspect with no advance warning. The following sequence shall be displayed when the starting signal is off while the signal immediately beyond remains at danger: ellow ed When the starting signal is off while the second signal beyond the starting signal is at danger, the following sequence shall normally be displayed: reen ellow ed The preceding sequence shall not be displayed where the yellow aspect alone would provide insufficient forewarning of the red aspect, given the required signal spacing, and the acceleration and braking characteristics of trains; in such cases the starting signal shall display a double yellow aspect when off. 5.2 Aspect Sequences for Advance Warning of Diverging oute Flashing ellow Aspects Advance warning of diverging route may be conveyed by aspect sequences employing flashing yellow aspects. In three aspect signalling the flashing double yellow aspect shall not be displayed, and a flashing single yellow aspect shall only be displayed in the context of the following sequence: reen Flashing ellow ellow (Junction Signal) In four aspect signalling flashing yellow aspects shall only be displayed in the context of the following sequence: reen Flashing Double ellow Flashing ellow ellow (Junction Signal) Under no circumstances shall the sequences defined above be extended by displaying flashing aspects at a greater number of signals than shown. No signal shall be capable of displaying flashing aspects relating to more than one junction signal Splitting Distant Aspects Where advance warning of a diverging route is conveyed by an aspect sequence employing splitting distant aspects, the junction signal shall be free to display the aspect appropriate to the condition of the route ahead. The signal immediately prior to the junction signal shall display the splitting distant aspect appropriate to the aspect displayed by the junction signal and the route set. Where required, the signal preceding the inner splitting distant signal shall display the outer splitting distant aspect appropriate to the aspect displayed by the inner splitting distant signal and the route set from the junction signal. A I L T A C K 7

8 ailway roup Standard K/T0032 Page 8 of 13 Withdrawn Document Lineside Signal Aspect Sequences 5.3 Approach Control of Aspects Approach Control from ed Where a signal is approach controlled from red, the approach aspect sequence shall be identical to the sequence displayed when the signal is at danger for any other reason Approach Control from ellow Where a signal is approach controlled from yellow, a double yellow or flashing single yellow aspect shall be displayed at the preceding signal. Where there is a significant risk of reading through, the exit signal of the route from the approach controlled signal shall be held at red until such time as the approach controlled signal is required to clear from yellow. 5.4 Segregation of Three and Four Aspect Signalling The boundaries between sections of three and four aspect signalling shall be clearly identifiable and logical from the perspective of the driver. Normally these boundaries shall coincide with geographical junctions, or other locations at which there is an obvious change in traffic flow. However, parallel running lines signalled for movements in the same direction may also be considered as independent sections of line for this purpose. Where the boundaries between sections of three and four aspect signalling are less obvious, each section shall consist of a number of signals sufficient to establish a clear pattern of three or four aspect signalling No isolated three aspect sequence shall be displayed in a four aspect section of line, except where there is a signal which has no main signal route reading up to it, in which case the requirements of Clause shall apply Isolated four aspect sequences may be displayed in a three aspect section of line, subject to the constraints imposed by Clause No signal that is part of a continuous sequence of signals shall be capable of displaying a single yellow aspect as a first caution for one stop signal, and a double yellow aspect as a first caution for another stop signal applying to the same line, except as permitted by To enable compliance with this requirement where there is a transition from three to four aspect signalling, or where isolated four aspect signals are provided in a three aspect line, it shall be necessary to: provide a signal only displaying ed, Double ellow, and reen, and a signal only displaying ellow, Double ellow and reen; O approach control a signal from red. See Appendix A for illustration of this transition Where signalling is not continuous, a repeater signal may display a single yellow aspect as a first caution for one stop signal and a double yellow aspect as a first caution for another stop signal in the same line of route. 8 A I L T A C K

9 ailway roup Standard K/T0032 Lineside Signal Aspect Sequences Page 9 of 13 6 Semaphore Aspects 5.5 Semaphore Equivalent Aspect Sequence Where semaphore signals are replaced by colour light signals, and constraints on signal spacing prevent the use of the normal colour light aspect sequences, the aspect sequence principles for semaphore signalling shall be followed, with the proviso that a colour light stop signal used in these circumstances shall only display a green aspect when all stop signals ahead, up to and including the section signal, display green aspects. All stop signals other than the section signal shall be capable of displaying a yellow aspect. 6.1 Aspect Sequence Leading to a Stop Aspect Under normal operating circumstances, the minimum forewarning of a semaphore signal at danger shall be a distant signal caution aspect displayed at least minimum signal spacing distance from the stop aspect. Where a signal that is not the first stop signal beyond the distant signal is held at danger, the preceding stop signal shall be held at danger until such time as an approaching train is at or nearly at a stand. A distant signal off aspect shall only be displayed when all of the stop signals to which it applies are off. The distant signal shall normally be worked unless either, all trains stop, or there is a severe permanent speed restriction. In these cases it may be fixed at caution, subject to the approval of the Infrastructure Controller following an appropriate risk assessment. Where a distant signal arm is immediately followed by a stop signal to which the distant arm does not apply, a repeat distant arm shall be provided in association with that stop signal. 6.2 Aspect Sequence for Advance Warning of Diverging oute The distant signal shall not be capable of being cleared for a diverging route, except where it is a splitting distant signal. 7 Prohibited Aspect Sequences Where a semaphore splitting distant signal is provided, the appropriate distant signal arm may be off when the corresponding junction signal arm, and any other stop signals to which the distant signal applies, are off. The provision of intermediate stop signals between the distant signal and the junction signal for which the splitting distant signal applies shall be avoided wherever possible; however, where this situation is unavoidable, any intermediate stop signal shall be equipped with the same arrangement of distant signal arms as the splitting distant signal, and these distant arms shall be worked from the same signal box as the splitting distant signal. Successive signals shall not simultaneously display the following: a red aspect immediately preceded by any colour light aspect other than a single yellow aspect; a red aspect immediately preceded by a semaphore distant arm in the off position. A I L T A C K 9

10 ailway roup Standard K/T0032 Page 10 of 13 8 Miscellaneous Aspects and Indications Withdrawn Document Lineside Signal Aspect Sequences a flashing single yellow aspect immediately preceded by a signal displaying a flashing single yellow aspect; a flashing double yellow aspect immediately preceded by a signal displaying a flashing single yellow aspect or flashing double yellow aspect; a flashing double yellow aspect immediately followed by a signal displaying any aspect other than flashing single yellow; any sequence involving both a flashing colour light aspect and a semaphore signal; a semaphore stop signal arm in the on position preceded by a semaphore distant signal arm in the off position; a semaphore stop signal arm in the on position preceded by any colour light aspect other than the yellow aspect. 8.1 Stop Board Where a stop board requires a caution aspect, this may take the form of a colour light yellow aspect, a semaphore distant arm fixed in the on position, or a distant board. 8.2 Points Indicator A points indicator shall be preceded by a signal (at the appropriate signal spacing distance) displaying a caution aspect when the points are not correctly set, except where all trains start from the rest within sight of the indicator. The caution aspect may take the form of a colour light yellow aspect, semaphore distant signal arm in the on position, or distant board. 8.3 Buffer Stop A buffer stop shall be regarded as a stop aspect, and the cautionary aspect, or aspect sequence, appropriate to the prevailing type of signalling (ie. colour light or semaphore) shall be displayed on the approach. In semaphore areas a distant board may be provided. 8.4 emote round Frame Marker Board Where a facing point marker board is provided, it shall be preceded by a worked distant signal. The distant signal shall be positioned at least minimum signal spacing distance prior to the facing point marker board. 10 A I L T A C K

11 ailway roup Standard K/T0032 Lineside Signal Aspect Sequences Page 11 of 13 eferences K/T 0031 K/T 0034 Lineside Signals and Indicators Signal Spacing A I L T A C K 11

12 ailway roup Standard K/T0032 Page 12 of 13 Withdrawn Document Lineside Signal Aspect Sequences Appendix A Illustration of Transition from 3 to 4 Aspect Signalling Permitted: Signal 4 approach controlled from red when signal 5 at red #1 #1: approach control condition Permitted: Additional signal 4 provided A I L T A C K

13 ailway roup Standard K/T0032 Lineside Signal Aspect Sequences Page 13 of 13 Not Permitted: Signal 3 providing first caution for both signal 4 and signal A I L T A C K 13

Lineside Signal Aspect and Indication Requirements

Lineside Signal Aspect and Indication Requirements Synopsis This document mandates the appearance of lineside signalling system displays and the information they convey. This document contains one or more