signalling design principle - overlaps€¦ · signalling design principle - overlaps version 1.0...

Signalling Design Principle - Overlaps

T HR SC 10004 ST

Standard

Version 1.0

Issue date: 04 June 2018

© State of NSW through Transport for NSW 2018

T HR SC 10004 ST Signalling Design Principle - Overlaps

Version 1.0 Issue date: 04 June 2018

Important message This document is one of a set of standards developed solely and specifically for use on

Transport Assets (as defined in the Asset Standards Authority Charter). It is not suitable for any

other purpose.

The copyright and any other intellectual property in this document will at all times remain the

property of the State of New South Wales (Transport for NSW).

You must not use or adapt this document or rely upon it in any way unless you are providing

products or services to a NSW Government agency and that agency has expressly authorised

you in writing to do so. If this document forms part of a contract with, or is a condition of

approval by a NSW Government agency, use of the document is subject to the terms of the

contract or approval. To be clear, the content of this document is not licensed under any

Creative Commons Licence.

This document may contain third party material. The inclusion of third party material is for

illustrative purposes only and does not represent an endorsement by NSW Government of any

third party product or service.

If you use this document or rely upon it without authorisation under these terms, the State of

New South Wales (including Transport for NSW) and its personnel does not accept any liability

to you or any other person for any loss, damage, costs and expenses that you or anyone else

may suffer or incur from your use and reliance on the content contained in this document. Users

should exercise their own skill and care in the use of the document.

This document may not be current and is uncontrolled when printed or downloaded. Standards

may be accessed from the Transport for NSW website at www.transport.nsw.gov.au

For queries regarding this document, please email the ASA at

[email protected] or visit www.transport.nsw.gov.au

© State of NSW through Transport for NSW 2018



Standard governance

Owner: Lead Signals and Control Systems Engineer, Asset Standards Authority

Authoriser: Chief Engineer, Asset Standards Authority

Approver: Executive Director, Asset Standards Authority on behalf of the ASA Configuration Control Board

Document history

Version Summary of changes

1.0 First issue.

© State of NSW through Transport for NSW 2018 of 36



Preface The Asset Standards Authority (ASA) is a key strategic branch of Transport for NSW (TfNSW).

As the network design and standards authority for NSW Transport Assets, as specified in the

ASA Charter, the ASA identifies, selects, develops, publishes, maintains and controls a suite of

requirements documents on behalf of TfNSW, the asset owner.

The ASA deploys TfNSW requirements for asset and safety assurance by creating and

managing TfNSW's governance models, documents and processes. To achieve this, the ASA

focuses on four primary tasks:

• publishing and managing TfNSW's process and requirements documents including TfNSW

plans, standards, manuals and guides

• deploying TfNSW's Authorised Engineering Organisation (AEO) framework

• continuously improving TfNSW’s Asset Management Framework

• collaborating with the Transport cluster and industry through open engagement

The AEO framework authorises engineering organisations to supply and provide asset related

products and services to TfNSW. It works to assure the safety, quality and fitness for purpose of

those products and services over the asset's whole-of-life. AEOs are expected to demonstrate

how they have applied the requirements of ASA documents, including TfNSW plans, standards

and guides, when delivering assets and related services for TfNSW.

Compliance with ASA requirements by itself is not sufficient to ensure satisfactory outcomes for

NSW Transport Assets. The ASA expects that professional judgement be used by competent

personnel when using ASA requirements to produce those outcomes.

About this document

This standard forms part of the TfNSW suite of railway signalling principles which detail the

requirements and design principles. This standard specifically covers overlaps.

To gain a complete overview of signalling design requirements, this document should be read in

conjunction with the suite of signalling design principle standards.

This standard covers requirements for the provision of overlaps associated with ends of

authority.

This standard supersedes RailCorp document ESG 100.4 Overlaps, version 1.7.




The changes to previous content include the following:

• clarification to existing requirements and the provision for the implementation of ETCS

Level 1 LS (limited supervision) mode

• replacement of RailCorp organisation roles and processes with those applicable to the

current TfNSW organisational context

• conversion of the standard to ASA format and style

This standard is a first issue.




Table of contents 1. Introduction .............................................................................................................................................. 8

2. Purpose .................................................................................................................................................... 8 2.1. Scope ..................................................................................................................................................... 8 2.2. Application ............................................................................................................................................. 8

3. Reference documents ............................................................................................................................. 9

4. Terms and definitions ............................................................................................................................. 9

5. Core principles for overlaps ................................................................................................................... 9 5.1. Rail vehicle detection ........................................................................................................................... 10 5.2. Overlap distance .................................................................................................................................. 10

6. Overlaps in trainstop territory .............................................................................................................. 11 6.1. Overlap distance in trainstop territory .................................................................................................. 11 6.2. Variation to overlap distances in trainstop territory.............................................................................. 12 6.3. Applicable line speed ........................................................................................................................... 12 6.4. Overlaps for trains that operate to high speed boards ........................................................................ 13

7. Reduced overlaps .................................................................................................................................. 13 7.1. Requirements for a conditional caution aspect.................................................................................... 14 7.2. Conditional caution aspects around platforms..................................................................................... 15 7.3. Requirements for a conditional low speed aspect ............................................................................... 15 7.4. Requirements for low speed aspects .................................................................................................. 16

8. Overlaps for subsidiary or ground shunting signals ......................................................................... 17

9. Overlaps where ETCS level 1 LS mode is provided........................................................................... 18

10. Locking opposing routes leading into or situated within an overlap .............................................. 18

11. Setting and locking of points within an overlap ................................................................................. 19 11.1. Trailing points .................................................................................................................................. 19 11.2. Facing points ................................................................................................................................... 21 11.3. Facing points providing flank protection .......................................................................................... 22 11.4. Special arrangements ...................................................................................................................... 23

12. Preferential setting of points in an overlap ........................................................................................ 23

13. Automatic overlap setting by track circuit .......................................................................................... 26

14. Overlap swinging ................................................................................................................................... 27

15. Overlap maintenance ............................................................................................................................ 27

16. Obsolete requirements ......................................................................................................................... 28 16.1. Overlaps for running signals not equipped with trainstops .............................................................. 28 16.2. Overlaps for single lines and crossing loops ................................................................................... 30 16.3. Setting and locking of points within an overlap at crossing loops ................................................... 33 16.4. Overlaps in ETS and OTS territory where running signals are provided ........................................ 34




Appendix A Braking curves used for overlaps – minimum predetermined distance ...................... 36




1. Introduction An overlap is a safety margin provided beyond an end of authority.

The purpose of an overlap is to ensure a margin of safety beyond a stop signal by establishing

a predetermined separation distance between two trains.

2. Purpose This document specifies the requirements and design principles for overlaps to minimise the

likelihood of collision or infrastructure damage if a train were to pass a signal at stop.

2.1. Scope This document defines the concepts and definitions for various components of overlaps.

This document provides requirements for the following:

• distance and variations to overlap distance

• trainstop territory

• braking curves

• applicable line speed

• conditional overlaps

• low speed overlaps

• overlaps for subsidiary and ground signals

• overlaps where European train control system (ETCS) L1 limited supervision (LS) mode is

provided

• points within the overlap

• overlap maintenance

• obsolete requirements

2.2. Application This standard applies to Authorised Engineering Organisations (AEOs) engaged to carry out the

preliminary and detailed signal design for new and existing installations in the rail passenger

network.




The rail passenger network is within the area bounded by Newcastle (in the north), Richmond

(in the northwest), Bowenfels (in the west), Macarthur (in the southwest) and Bomaderry (in the

south), and all connection lines and sidings within these areas, but excluding private sidings,

freight lines and non-electrified lines.

3. Reference documents The following documents are cited in the text. For dated references, only the cited edition

applies. For undated references, the latest edition of the referenced document applies.

Transport for NSW standards

T HR RS 00100 ST RSU 100 Series – Minimum Operating Standards for Rolling Stock –

General Interface Standards

T HR RS 00830 ST RSU Appendix C – Brake Performance Curves

4. Terms and definitions The following terms and definitions apply in this document:

AEO Authorised Engineering Organisation

ASA Asset Standards Authority

ATP automatic train protection

CTC centralised traffic control; a system of working whereby the signals and points at adjoining

signalled sections that are operated remotely from a centralised train control centre

ETCS European train control system

service speed a calculated or observed speed less than the permitted speed. The speed is the

most practical, achievable speed based on braking and acceleration characteristics of rolling

stock (with due consideration to performance of future rolling stock), speed limits and track

gradient on the approach to the signal.

5. Core principles for overlaps An overlap is the section of track immediately in advance of a stop signal, which is required to

be unoccupied, have all points in the overlap lined up and no conflicting movements authorised,

before the stop signal in the rear is permitted to show a proceed indication.

Where required for operational purposes in closing up trains, the overlap may be reduced or

omitted entirely as long as mitigations are in place to control the approach speed of the train

approaching the signal at stop.




5.1. Rail vehicle detection Where the method of safeworking utilises rail vehicle detection, rail vehicle detection of the track

up to the predetermined overlap (minimum distance) shall be included in the controls of the

running signals.

Site constraints, existing infrastructure and route controls should be considered when defining

the overlap track circuit locations. To avoid unnecessary moving or installing additional

equipment, track circuits or axle counter sections which extend beyond the predetermined

overlap distance may be used as the overlap if there is no adverse operational outcome from

having a longer overlap. Examples include where the overlap is only a short distance before the

next signal or other infrastructure such as a level crossing, or where converging routes with

different approach speeds require different overlap minimum distances on a common line.

On a plain line in track circuited areas, this shall be at least the 'A' track circuit beyond a stop

signal.

5.2. Overlap distance The overlap distance is the length of the section of track which forms the overlap. The overlap

distance is measured from the stop signal to a predetermined clearing point in advance.

The following factors can influence the determination of the clearing point:

• historical precedents and experimental data

• maximum line speed

• permanent speed restrictions

• service speed (shall not consider train service stopping patterns)

• emergency braking curves

• gradient

• emergency brake tripping system

• automatic train protection (ATP)

• approach speed control by conditional caution, low speed, conditional low speed or

intermediate trainstops




6. Overlaps in trainstop territory Section 6.1 to Section 7.4 addresses the requirements for the provision of overlaps at running

signals which are equipped with trainstops for both above and below ground sections of the

network.

If a running signal on a passenger line is capable of showing an unconditional warning aspect,

then an overlap shall be provided immediately beyond the stop signal to which the warning

aspect applies.

6.1. Overlap distance in trainstop territory The length of the overlap shall be determined by the relevant trip stop braking curve for double

deck suburban R sets and S sets for trains operating at the permissible line speed applicable to

the particular section of line concerned.

Maximum crush load braking distances for a trip stop shall be used to determine the overlap

distance in underground areas where the severity of an incident following a signal passed at

danger (SPAD) is increased due to the confinement of the space. However, where a reduced

speed is used, an acceleration allowance shall be included in the overlap speed determination.

The acceleration allowance shall be based on the following factors:

• the train accelerating at maximum acceleration from the location of any previous speed

check (usually a trainstop)

• the maximum speed obtained at the stop signal (or raised speed checking trainstop) as a

result of this acceleration

• the maximum line speed being applied

Where the train speed is proven by approach control of trainstops, the overlap distance

determined from the appropriate brake curve may be in accordance with the lower approach

speed. Where intermediate trainstops are used, the overlap distance is measured from the next

speed checking trainstop (which will not necessarily be at stop).

For all above ground areas, the average crush load braking distance for a trip stop is adopted.

Refer to Appendix A for a selection of braking curves to be used for overlap design on specific

sections of track.

For further information on braking requirements, including GE52 and GE52A brake curves, refer

to T HR RS 00830 ST RSU Appendix C – Brake Performance Curves and

T HR RS 00100 ST RSU 100 Series – Minimum Operating Standards for Rolling Stock –

General Interface Standards.




If the service speed is less than the line speed, the service speed for the determination of the

overlap length may be permitted for use. However, effective arrangements shall be in place to

ensure trip-fitted trains with higher service speeds. Longer braking distances shall not be

introduced to run on the line without a proper risk analysis.

6.2. Variation to overlap distances in trainstop territory If the line headway is adversely affected by the overlap distance in a particular section, then a

reduction of the overlap distance may be investigated based on the appropriate factors detailed

in Section 5.2, provided that the proposed alternative is SFAIRP.

6.3. Applicable line speed In accordance with the requirements detailed in Section 5, the line speed shall be used for the

determination of overlap distances using the applicable brake curve. A risk based approach

shall be followed to assess the potential speed at line speed changes and when turnouts are

present.

The following describes different scenarios, where the speed used to calculate the required

overlap length may be adjusted:

• Turnout exists in the overlap

To avoid unnecessary overlap lengths for a turnout route based on the turnout speed being

significantly less than the straight route and with consideration to derailment speeds at

turnouts generally be classified as twice the turnout speed.

Where a turnout exists in the overlap, the approach speed used to determine the overlap

length shall be the turnout speed where only ETCS fitted rolling stock operates and turnout

protection is provided.

For all other scenarios, twice the turnout speed or line speed for the straight route,

whichever is lesser, shall be used.

• Train approaches through a turnout

Where a train approaches a signal at stop through a turnout, the overlap may be

determined using the turnout speed (that is, the line speed for that approach).

• Speed board increase prior to a signal

Where a speed board increases the speed in the block prior to a signal at stop, the lower

approach speed leading up to this board, provided it is within the restrictive aspect

sequence shall be used.




• Speed board decrease prior to signal

Where a speed decrease occurs in the block prior to the signal at stop, the higher

approach speed leading up to the board shall be used with the following exceptions:

o the track configuration physically limits the speed

o the board is further than 300 m from the signal (it is assumed that a driver within an

approaching distance of 300 m will successfully achieve the reduced speed prior to

reaching the signal at stop)

o additional controls are in place to maintain the lower line speed at the signal at stop

6.4. Overlaps for trains that operate to high speed boards XPT, Endeavour, Xplorer, Hunter and more recent electric multiple unit trains may be permitted

to run to high speed boards. The overlaps shall be based on GE52A in train stop fitted areas for

speeds up to 130 km/h.

The designed GE52A overlap requirements may not be achievable due to any of the following

factors:

• track layout

• the required length is a constraint on headway or line speed

• line speeds used are greater than 130 km/h but less than 160 km/h

The GX2M curve may be used in lieu of the GE52A curve to determine the overlap length for

the high speed board if the train speed exceeds the medium speed board overlap requirement.

Refer to T HR RS 00830 ST for GX2M braking characteristics.

7. Reduced overlaps Conditional (reduced) overlaps are provided on running signals when the full overlap is not

available.

If trains are required to be brought closer together for operational and headway reasons, a

conditional overlap may be provided in lieu of a full overlap, to enable a running signal to

conditionally clear and display a conditional caution aspect.

Conditional clearing is a useful tool in the approach control of train speed.

The benefits include being able to use existing signal aspects and the control applies to all

trains. This is important where non-trip fitted trains operate as a displayed aspect with the

trainstop in the raised position does not have the same speed reduction impact to the driver as




a 'stop' indication. However, if an aspect is permanently conditional, a risk that drivers can

anticipate the clearing and may not be prepared to stop at the signal can exist. This can result in

a SPAD. Where only trip fitted trains operate, the train stop enforces the stop signal such that

any SPAD has a safe result. However, the arrangement can mislead drivers and where unfitted

trains operate, the train approach speed is not checked and can result in inadequacy of the

overlap.

Consequently, conditional clearing shall be used on a signal that is usually cleared to a full

running aspect and that the conditional clearing is only in force whenever the condition exists

that requires its use. The length of the timing track for conditional clearing speed checking

should be kept consistent and within the range of 160 m to 220 m.

Full use of the available overlap should be made, so that if it is suitable for a higher speed, then

the timing should reflect the higher speed.

7.1. Requirements for a conditional caution aspect The running signal requiring the full overlap shall be cleared after a suitable time delay has

elapsed (following the initial occupancy of the berth track circuit) if the following conditions are

present:

• the signal spacing is less than 500 m with an overlap of reduced distance to 100 m is

known to be clear

• the train ahead occupying part of the full overlap distance is stationary or signalled away in

the correct direction of running

This ensures that the speed of the following train has been reduced to be commensurate with

the safety margin provided by the reduced overlap distance. See Figure 1 for an arrangement of

conditional overlaps.


Figure 1 - Conditional overlaps

Where the signal spacing is greater than 500 m, a reduced overlap distance of 200 m shall be

proved to be clear or signalled away prior to the running signal that requires the full overlap



stepping up to a conditional caution aspect, and after the berth track circuit occupancy has

timed out.

7.2. Conditional caution aspects around platforms Conditional cautions that are not typically part of the normal aspect sequence should be

provided (where required by the operational requirements) to close up trains at platforms.

The provision of conditional cautions presents risks that shall be assessed as part of the

application.

At platform departure signals, a train approaching a signal at stop shall meet the timing

requirements for the clearing of the signal; however, the driver will have no indication as to

whether a full or reduced overlap is provided at the stop signal.

A risk assessment shall be carried out when providing conditional caution aspects.

7.3. Requirements for a conditional low speed aspect A reduced overlap shall be provided for the provision of train movements made under the

control of a low speed indication on a running signal to facilitate trains in a section that are close

to one another.

The length of an overlap associated with a low speed aspect shall be at a distance less than

100 m (including zero) where required by operations. Track circuits in the overlap shall be

proved clear, consistent with the low speed route, to ensure adequate protection between trains

is maintained.

Depending on circumstances governing the overlap condition, intermediate train stops shall be

provided for additional speed control in addition to the low speed indication.

Note: The speed that the intermediate trainstops have been set at is not readily

apparent to the driver. Current practice is to provide intermediate train stop advisory

speed boards to indicate the speed at which trains may pass.

The low speed aspect shall be cleared after the berth track circuit has been occupied for an

appropriate period of time. This is to ensure that the train speed has been suitably reduced to a

speed that is commensurate with the overlap distance available where the full overlap is not.

The low speed aspect shall only clear in conjunction with the clearing of the train stop at the

signal.

A locking overlap coincidental with the overlap for the caution aspect of the running signal with

which the low speed indication is associated, shall be provided. Locking overlaps used with




conditional low speed indications may be considered for reduction to meet special operational

requirements on obtaining special approval.

See Figure 2 for an example of the low speed overlap arrangement.

LOCKING OVERLAP

(OL DISTANCE 0-100m)

(OL DISTANCE100-200m)

(OL DISTANCE,AS PER BRAKE CURVE)

OCC TIME t3TRACK CIRCUIT

(ITS SPEED CHECKING)

SIGNAL SPACING <500m

(CONDITIONAL)

(APPLICABLE TO BOTH CONDITIONAL & LOW SPEED ASPECTS)

Figure 2 - Running signal overlap arrangements

7.4. Requirements for low speed aspects A reduced overlap shall be provided for the provision of train movements made under a running

low speed in designated low speed territories where the permitted speed at the running signal is

25 km/h.

Low speed areas include the following:

• City underground

• Eastern Suburbs Line

• North Shore

• Sydney-Strathfield area




An overlap length of 100 m is required for a low speed route. Track circuits in the overlap shall

be proved clear consistent with the low speed route to ensure adequate protection between

trains is maintained.

A locking overlap shall be provided that is commensurate with the caution clearance point of the

associated signal.

Intermediate trainstops should be considered for low speed movements, pending circumstances

that govern the overlap conditions such as existing infrastructure, access and space.

8. Overlaps for subsidiary or ground shunting signals A locking overlap shall be provided for train movements associated with subsidiary or ground

shunting signals in running signal territory. A locking overlap shall be provided whether the

shunt signal takes the form of a subsidiary aspect on a running signal or a ground shunt signal.

A nominal locking overlap of 100 m on a running line shall be provided for a subsidiary shunting

indication or ground shunting signal indication.

If necessary, the shunt signal requiring the overlap shall set, lock and maintain one or more sets

of points in the locking overlap. This is to eliminate the possibility of converging or opposing

movements obstructing the overlap once established, particularly where the opposing

movement is a main route.

In yards, points in the overlap are not normally locked. Routes that share an overlap through

trailing points shall lock each other directly. Where signal moves are not present through the

ground frame, the outer signal shall lock the ground frame directly. The locking shall not be

maintained after the shunt route has cleared.

Where speeds are restricted, the locking overlap distance may be reduced to 60 m or braking

distance from the stop signal whichever is greater. For directly opposing movements between

low speed shunt routes, the shared overlap may be reduced to three quarters of the combined

distance of the individual overlaps. However, the 60 m minimum overlap (or braking distance

overlap, if less) shall be applied to any converging movements.

Overlap track circuits shall not be proved clear in shunting signal aspects.




9. Overlaps where ETCS level 1 LS mode is provided Where ETCS level 1 limited supervision (LS) mode is overlayed to an existing signalling system,

consideration should be given to the existing layout.

For new works and where unfitted rolling stock operates over ETCS fitted track, the principle for

the minimum overlap distance in trainstop territory shall be maintained.

LS mode shall not be used to reduce overlap distance or the removal of conditional overlaps.

LS mode is the European railway traffic management system (ERTMS) and ETCS onboard

equipment mode that provides partial protection against over speed and over run. The driver

shall observe and obey to line side signals and operating rules when operating in LS mode.

For retrofit installations, where an existing overlap distance is deficient against the requirements

of Section 5 and Section 6, a risk based approach shall be adopted when assessing the

deficiency. Alterations to the existing infrastructure, additional speed controls or the provision of

ETCS shall be used as SPAD mitigation. Where ETCS is used, the approach speed of the train

shall be controlled to ensure that the emergency braking distance from the signal is less than or

equal to the overlap distance, based on the more conservative brake curve applicable to that

section of line.

10. Locking opposing routes leading into or situated within an overlap If a signal requires an overlap into which a route or overlap from an opposing signal leads or in

which the route from an opposing signal is situated, then the opposing route shall be normal.

Any associated track circuit holding is released, if applicable, before the particular route of the

signal requiring the overlap is permitted to set.

The route holding will be placed at the route level (RUR) and be normally released after a time

release (if routes are leading or situated in the overlap). See Figure 3 for an example of this

arrangement.




Figure 3 - Locking and releasing of opposing routes in an overlap

11. Setting and locking of points within an overlap Section 11.1 to Section 11.4 addresses the requirement for setting and locking of trailing and

facing points when situated within an overlap and for trapping and flank protection to an overlap.

11.1. Trailing points If a set of trailing points situated within an overlap is available, then the points shall be set or

locked in the appropriate position by the particular route of the signal requiring the overlap. The

points shall remain locked until the particular route has been normalised, or where provided, an

alternative overlap has been set.

If a train passes the signal requiring the overlap, then the trailing points shall become locked in

position by any of the following conditions:

• by track circuit occupancy in the route until the train has come to a stand at the signal in

advance and any time release provided has expired

• where provided, an alternative overlap has been set




• the train has passed beyond the signal in advance and the trailing points have become

directly locked by track circuit occupancy

See Figure 4 for an example of this arrangement.


Figure 4 - Setting or locking of points in an overlap

If alternative overlaps are provided due to a diverging route, then the set of trailing points shall

be set and locked, subject to the particular boundaries of the overlap. See Figure 5 for an

example of this arrangement.




If a set of trailing points situated within an overlap is not available, then the particular route of

the signal requiring the overlap shall be inhibited from being set.

11.2. Facing points If a set of facing points is situated within an overlap and each of the alternative overlaps are

available, then no setting or locking of the facing points is required.

If a set of facing points is situated within an overlap and one of the alternative overlaps is not

permitted or is not available, then the facing points shall either be set or locked, or both when

the following conditions are met:

• set/locked in the direction of the available overlap by the particular route of the signal

requiring the overlap

• remain locked until the particular route has been normalised or until an alternative overlap

has become available






If a train passes the signal requiring the overlap, then the facing points shall remain locked in

position for the following conditions:

• where required, by track circuit occupancy until the train has come to a stand at the signal

in advance and any time release provided has expired

• the train has passed beyond the signal in advance and the facing points have become

directly locked by track circuit occupancy

If a set of facing points situated within an overlap is not available to be set, then the particular

route of the signal requiring the overlap shall be inhibited from being set.

11.3. Facing points providing flank protection If a set of facing points which provides flank protection to an overlap is available, then it shall be

set or locked in the appropriate position by the particular route of the signal that requires the

overlap. The points shall remain locked until the particular route has been normalised, or where

provided, an alternative overlap has been set.

If a train passes the signal requiring the overlap, then the points shall be locked in position

based on the following conditions:

• by track circuit occupancy until the train has come to a stand at the signal in advance and

any time release provided has expired




• if the train has passed beyond the signal in advance and the points have become directly

locked by track circuit occupancy


If alternative overlaps are provided, then a set of facing points providing flank protection shall be

set and locked as described in the preceding paragraphs, subject to the particular arrangement

of the overlap. See Figure 5 for an example of this arrangement.

If a set of facing points which provides flank protection to an overlap is not available, then the

particular route of the signal requiring the overlap shall be inhibited from being set.

11.4. Special arrangements Under certain circumstances, special arrangements may be permitted for the setting of overlap

conditions. For example, the provision of dedicated push buttons may be used to enable special

arrangements to be invoked.

12. Preferential setting of points in an overlap When facing points exist in an overlap and the overlap set with those points in a given lay

requires other points to be set and locked in a particular lay, then the following options are

present in establishing the overlap:

• the facing points shall be set and locked so that the overlap is not affected by the other

sets of points

• one or more of the other points shall be set and locked to provide a useable overlap

This is known as conditional locking. Refer to Figure 7 for an example of this arrangement.

Figure 7 - Route setting – straight route most frequently used

In Figure 7, if 101 is normal, then 21(M) requires 102 normal and if 102 is reverse, then 21(M)

requires 101 reverse. If 101 is normal and free, and 102 is reverse and free, then with no other

constraints setting 21(M) would call both 101 reverse and 102 normal. However, it is only

necessary to call one or the other in order to establish a useable overlap.

In such cases, a priority or preference shall be determined to prevent the interlocking

unnecessarily calling multiple sets of points.




The following shall be included when determining preferences:

• function or relative importance of the different tracks – main lines would normally take

higher priority than crossovers, branches or sidings

• planned or actual operational patterns – if there is a meaningful majority of traffic using one

route rather than the other, this could justify a different first preference

• conflicts with other tracks or routes – it would normally be preferable to select the overlap

that impacts the least number of other tracks and routes, particularly to avoid conflict with

the routes that are operationally most likely to be used

• number of points that would be called – normally the preference would be to move the

smallest number of points unless there is justification for another option

• likely and unlikely conditions under which particular points might be locked

The first preference is normally to establish the overlap in the direction of the most frequently

used route ahead of an inner signal; this reduces the risks against the following:

• the probability of an overlap being set in the least used direction

• excessive or unnecessary overlap swinging with other routes

• interaction with the established overlap from other routes being set

Refer to Figure 8 for an example of this arrangement.

Figure 8 - Route setting – divergent route most frequently used

Figure 8 shows through-traffic is routed on the mains and the locals are used primarily for traffic

to and from the branch, such that 724 and 725 are most frequently used reverse.




When setting 513(M), the first preference is to have 724 reverse, requiring 731 normal; if 731 is

reverse and not free, then 513(M) requires 724 normal. As setting 724 normal does not affect

any other tracks, this can be used as a second preference for automatically establishing the

overlap for 513(M).

Route control tables shall show conditional locking in brackets with numerical suffix that denotes

the order of preference. Refer to Table 1 for an example of a route control table.

Table 1 - Route control table example

Points lay Sets, locks and detects points

Normal [731 w 724R]1, [724 w 731R]2

Reverse Reverse conditional locking is not required

Figure 9 - Route setting – impact on other lines

Figure 9 shows that the first preference when setting 1(M) is to minimise impact on other

running lines (the Up Main) if 82 is normal, then 1(M) requires 81 normal. If 81 is reverse and

not free, then 1(M) would require 82 reverse.

However, 81 would not normally be locked reverse with 82 normal, so there may be a reason

that the interlocking should not automatically call 82 reverse (this is particularly relevant where

the control system includes automatic route setting functionality which may conflict with the

planned actions of the signaller); instead, 82 could be ‘locked and detected only’ – if the

signaller sets 82 reverse, then the interlocking will lock the points to use that overlap for 1(M);

however, if 81 is locked reverse with 82 normal then 82 will not be called and 1(M) route simply

cannot set.

Special notations for the points which are conditionally called on setting the route are not

provided on control tables. The order of preference is shown on complex layouts involving a

combination of preferences and ‘lock and detect only’, but the ‘lock and detect only’ is shown

with a suffix ‘@’.

An example of the route control table is provided in Table 2.




Table 2 - Route control table example

Points lay Sets, locks and detects points

Normal [81 w 82N]

Reverse [82 w 81R]@

13. Automatic overlap setting by track circuit The automatic overlap setting is provided due to the occupation of track circuits in the

alternative overlap at the time a route is set.

This form of automatic overlap setting is provided when an outer running signal has a choice of

two or more overlaps beyond an inner signal and when one of the overlaps is not available (due

to track circuit occupation). Under these conditions, the facing points may be set towards the

available overlap automatically when the route is being set.

The outer signal shall set and lock the facing points in the direction for which the overlap is

available if the following conditions are present:

• a route from an outer signal to an inner signal has alternative overlaps

• the overlap for the direction of the facing points that are set is not available due to

occupancy of the overlap track circuits (at the time the route is being set)

See Figure 10 for an example showing this arrangement.


Figure 10 - Automatic overlap setting by track circuit occupation

These arrangements may become overly complicated if two or three sets of facing points are

involved and multiple overlap choices are available. Care should be exercised to restrict the

overlap swinging to the minimum to satisfy traffic conditions. Overlaps shall not be automatically

set across opposing roads.

Details of the overlap setting shall be shown on the points control table sheets applicable.



14. Overlap swinging Overlap swinging is provided to assist an operator to establish routes which interacts with one

or more overlaps previously set for one or more routes. This avoids the operator from having to

manually establish the alternative overlaps by individual point key movements before the route

to be set becomes available. This may become a complex and time consuming operation where

two or more junctions overlap and several routes have already been set.

If one or more routes have already been set and the appropriate overlaps established with the

signals displaying proceed aspects, other routes may be required to be set. If another route is

required to be set which can alter the lay of one or more sets of points in the overlaps of the

previously cleared signals, then the route which is to be set shall adjust the lay of the

established overlaps progressively. Adjusting the lay of the overlaps proves that an alternative

overlap is available before the facing points leading towards the alternative overlap are reset to

opposite lay.

If several sets of points are involved, then this process of overlap swinging shall be enforced by

the setting and locking of the overlap points in sequence.

Where multiple sets of points are involved, sequencing the setting and locking of the points may

be necessary to ensure that valid overlaps are available at all times for a signal already

displaying a proceed aspect and a train is already within the route. Signal aspect controls shall

continuously prove that a valid overlap is established.

15. Overlap maintenance Facing points locking is provided to ensure that a clear overlap is maintained while an

alternative overlap is occupied and a route is set or a train is occupying the route leading up to

the home signal at the points.

This locking is provided when an outer running signal has a choice of two or more overlaps

beyond an inner signal, and due to track circuit occupation, one (or more) of the overlaps is not

available.

If a choice of overlap exists beyond an inner signal, then the clearing of an outer signal will lock

any facing points beyond the inner signal to prevent the operation of those points towards the

obstructed overlap.

The points shall remain locked whenever a train is approaching the inner signal, and the

alternative overlap remains obstructed.

This locking may be released in any of the following conditions:

• when the alternative overlap becomes clear




• the route has been cancelled and the approach locking released

• the train has been time released at a stand at the inner signal

If multiple overlaps exist, care should be exercised to ensure that overlap maintenance is

properly applied through the various combinations of conditions.

Details of overlap maintenance locking shall be shown on the point's control table, as shown in

Figure 11.

Figure 11 - Overlap maintenance

16. Obsolete requirements Section 16.1 through to Section 16.4 identifies the existing requirements associated with the

provision of overlaps, not currently maintained for new works; however, these requirements may

be considered for retrofit alterations.

16.1. Overlaps for running signals not equipped with trainstops Section 16.1.1 through to Section 16.1.3 addresses the requirements for the provision of

overlaps on double lines at running signals that are not equipped with physical contact type or

ETCS train stops.

If a running signal on a passenger line is capable of showing an unconditional warning aspect,

then an overlap shall be provided immediately beyond the stop signal to which the warning

aspect applies.




16.1.1. Overlap distance for running signals not fitted with trainstops The nominal length of the overlap shall not be less than the minimum distances as shown in

Table 3.

Table 3 - Nominal length of overlap for running signals not fitted with a train stop

Speed range over a particular section or line

Minimum overlap distance

Less than or equal to 60 km/h Longest braking distance or 300 m, whichever is greater

61 km/h to79 km/h Longest braking distance or 400 m, whichever is greater

Greater than 80 km/h Longest braking distance or 500 m, whichever is greater

16.1.2. Variations to overlap distance for running signals not fitted with train stops If the grade on a particular section of line is greater than 1 in 100 falling, then the overlap

distance shall be increased by a minimum of 100 m for that speed range.

If a block joint already exists or is to be provided for other purposes and could also be used as

an overlap block joint without adversely affecting the line headway, then the overlap distance

may be increased to avoid the provision of a separate overlap track circuit.

If the line headway is adversely affected by the nominal overlap distance, then a reduction in

the overlap distance should be considered based on the appropriate factors presented under

Section 5.2.

Where train speeds are permanently restricted (for example, when trains are departing yards or

negotiating turnouts or junctions), then the overlaps beyond the signal may be reduced to 90 m

where the speed approaching the signal is restricted to 15 km/h, and to 150 m where the speed

is restricted to 25 km/h, or reduced to the longest braking distance, if less.

If a running signal is more than 1.5 km long and more than one and a half times the service

braking distance from the next signal, then the overlap distance for that running signal beyond

the next signal shall be commensurably greater than the normal minimum overlap distance.

16.1.3. Overlaps in isolated trainstop fitted areas Trainstops may be installed in isolated areas where a safety benefit is required to be realised,

without necessarily adjusting existing overlaps. However, when significant configuration

changes occur in these areas, the overlap distance requirements shall be implemented. Overlap

distances shall be adjusted to conform to GE52A or a risk assessment carried out to provide




additional controls where required, such as controlling the approach speed or changing existing

infrastructure accordingly.

16.2. Overlaps for single lines and crossing loops Section 16.2.1 and Section 16.2.2 address the requirements for the provision of overlaps on

single lines and crossing loops in running signal territory, not fitted with trainstops.

16.2.1. Provision of an overlap on a single line An overlap shall be provided at the exit from a single line block section immediately in advance

of the home signal.

This overlap shall extend from the home signal as far as the opposing main and loop starting

signals controlling the entrance to the single line block section and shall incorporate loop and

flank protection. Refer to Section 16.3 for details of the locking arrangements.

If only a home signal is provided, then a nominal overlap of 200 m shall be provided for the

single line block section extending over the loop end. If main running signals are provided for

loop entry, this distance shall be 300 m.

Refer to Figure 12 for an example of this arrangement.


Figure 12 - Home signal overlap on single lines

If an outer home signal is provided for operational reasons at the exit from a single line block

section together with an opposing starting signal on the single line, then an overlap shall be

provided immediately in advance of the outer home signal.

This overlap shall extend from the outer home signal towards the opposing starting signal on

the single line.



If an outer home signal is provided, then a nominal overlap of 500 m shall be provided for the

single line block section, with an additional 100 m overlap provided immediately in advance of

the opposing starting signal.

If a block joint already exists or is required to be provided for other purposes, then the location

of the existing or proposed block joint may be used as the overlap limit only if the line headway

is not adversely affected. The overlap distance may be increased to avoid the provision of a

separate overlap track circuit.


Figure 13 - Outer home signal overlap on single lines

16.2.2. Provision of overlaps at crossing loops The home signal shall be provided with an overlap immediately in advance of the main and loop

starting signals into the single block section in advance. The overlap shall extend from the main

or loop starting signal into the single line section in advance as far as the opposing home signal.



Figure 14 - Overlaps in crossing loops in CTC territory



If a subsidiary shunt signal is fitted to a home signal, then it shall be provided with an overlap

immediately in advance of the main and loop starting signals into the single line block section.

The overlap shall extend from the main or loop starting signals into the single line block section

in advance towards the opposing home signal. The overlap shall be a locking overlap only. No

overlap track circuit control shall apply to the subsidiary shunt aspect.

If an outer home signal is provided, then an overlap shall be provided for the caution aspect.

The overlap shall extend from the home signal to the main or loop signals leading into the single

line block section in advance. See Figure 15 for an example of this arrangement.


Figure 15 - Overlaps in crossing loops in CTC territory

If a main or loop exit signal is fitted with a subsidiary shunt signal, then the subsidiary shunt

signal shall be provided with an overlap which extends towards the opposing outer home signal.

The overlap shall be a locking overlap only and no overlap track circuit control shall apply to the

subsidiary shunt aspect.

At crossing loops, the distance between the loop and main starting signals and the home signal

shall be 200 m for low speed entry and 300 m for a main running aspect. Refer to Figure 12 for

an example of this arrangement. The points shall be set to deflect any conflicting movement.

The overlap distance for a subsidiary shunt signal shall be a minimum of 100 m.

The overlap distance for an outer home signal shall comply with the requirements specified in

Section 16.1 and not greater than the distance to the main and loop signals leading into the

section in advance.



16.3. Setting and locking of points within an overlap at crossing loops Section 16.3.1 and Section 16.3.2 address the requirements for setting and locking points

situated within the various overlaps required for a subsidiary low speed route, shunt route and

outer home signals at a crossing loop.

16.3.1. Opposing outer home signal not provided If the starting signal ahead is not clear but the low speed indication fitted to the home signal is

required to be cleared for the main line, then the particular route shall set and lock the trailing

points in the overlap in the reverse position until the particular route is normalised. See

Figure 16 for an example of this arrangement.

Figure 16 - Setting and locking points in the overlap

This locking shall not be held by the occupation of track circuits.

The points shall be detected reverse before the signal is permitted to clear and continuously

thereafter until the route is normalised.

If the low speed aspect fitted to the home signal is required to be cleared for the loop, then the

particular route shall set and lock the trailing points in the overlap in the normal position until the

particular route is normalised. See Figure 17 for an example of this arrangement.


Figure 17 - Setting and locking points in the overlap

This locking shall not be held by the occupation of track circuits.



The points shall be detected normal before the signal is permitted to clear and continuously

thereafter until the route is normalised.

16.3.2. Opposing outer home signal provided

If the low speed aspect fitted to the home signal is required to be cleared for the main line or the

loop line and an opposing outer home signal is provided, then the particular route required shall

set and lock the trailing points in accordance with the requirements set out in Section 11 . Refer

to Figure 18 and Figure 19 for diagrams showing the arrangements for setting and locking

points in the overlap for 'A' and 'B' route sets.

Figure 18 - Setting and locking points in the overlap with outer home in 'A' route set

Figure 19 - Setting and locking points in the overlap with outer home in 'B' route set

This locking shall be held by the occupation of track circuits or released by track circuit

occupation for a predetermined time.

16.4. Overlaps in ETS and OTS territory where running signals are provided Overlaps are provided on single lines operated under electric train staff (ETS) and ordinary train

staff (OTS) regulations, and where running light home and starting signals are provided.

An ETS is a system of single-line safeworking in which a physical token is the normal authority

to enter the section. The system has a number of functionally identical tokens electrically locked

in instruments located at each entry or exit point of the section so that only one can be released

at a time. The name of the token used in the system of safeworking is also provided.




An OTS is a system of single-line safeworking in which a physical token is the normal authority

to enter the section. Only one physical token is provided and the name of the token used in the

system of safeworking is provided.

An overlap shall be provided at the exit from the single line section immediately in advance of

the home signal. The overlap shall extend from the home signal to the opposing starting signal

or signals controlling the entrance to the single line section or approved clearing point as

required. The length of the overlap in ETS and OTS territory shall be a minimum of 200 m.



Figure 20 - Overlaps in ETS or OTS territory



Appendix A Braking curves used for overlaps – minimum predetermined distance

Table 4 provides a selection of braking curves to be used for overlap design on specific sections of track. The breaking curves listed are only applicable to the rail

passenger network.

Table 4 - Breaking curves used for overlaps

Metropolitan region Section of line Applicable curve

Inner City Central - Circular Quay, Central – Waverton, Erskineville – Bondi Junction Central – Wolli Creek (New Southern Railway/Airport Line)

GE52 *include acceleration allowance

Inner City Central – Strathfield, Central – Meeks Road Junction (Tempe) GE52A

Illawarra Meeks Road Junction – Kiama and Port Kembla, Sutherland – Cronulla GE52A

North Strathfield – Hornsby - Woodville Junction - Wickham GE52A

West Strathfield – Emu Plains, Emu Plains – Lithgow, Flemington – Homebush Bay – Lidcombe (inc Olympic Park) Clyde – Carlingford, Blacktown – Richmond

GE52A

South Lidcombe – Cabramatta (via Sefton), Granville – Cabramatta, Tempe – Glenfield Cabramatta – Macarthur, Glenfield – Leppington

GE52A

North Shore Waverton – Hornsby GE52A

North Shore Chatswood – Epping GE52 *include acceleration allowance

Bankstown Sydenham - Sefton Park Junction GE52A


signalling design principle - overlaps€¦ · signalling design principle - overlaps version 1.0...

Documents