Impact assessment for changes to a Railway Group … IA02.pdf · RSSB impact assessment: RIS-0713-CCS Issue: Final Page 1 of 11 Impact assessment for changes to a Railway Group

RSSB impact assessment: RIS-0713-CCS Issue: Final Page 1 of 11

Impact assessment for changes to a Railway Group Standard

Version: Final

Date: December 2017

Relevant Railway Group Standards

Title: Lineside Signal Spacing and Speed Signage

Number: GKRT0075 Issue: Four

Synopsis: This document specifies the minimum distances that must be provided between the first cautionary aspect and the stop signal to which it applies. In addition, it addresses the signing for permissible speeds and speed restrictions.

Railway Group Standards withdrawn

Title: Proceed-on-Sight Authorities

Number: GERT8071 Issue: Two

Synopsis: This document mandates the requirements for the degraded mode signalling facility, known as a Proceed-on-Sight Authority (PoSA).

Title: Lineside Signals, Indicators and Layout of Signals

Number: GKRT0045 Issue: Five

Synopsis: This document defines the configuration and layout of lineside signalling equipment that is used to convey information to infrastructure managers operating stations, and railway undertaking personnel.

New Rail Industry Standard

Title: Lineside Signalling Layout Driveability Assessment Requirements

Number: RIS-0713-CCS Issue: One

Synopsis: This document sets out requirements for assessing the driveability of signalling systems and guidance on the process of assessing changes to signalling layouts or signal aspect sequences.

1 Executive summary

1.1 Rail Industry Standard (RIS) RIS-0713-CCS issue one ‘Lineside Signalling Layout Driveability Assessment Requirements’ sets out requirements for assessing whether a signalling layout is fit for purpose and is adequate to enable train drivers to perform their train driving responsibilities. The RIS also provides guidance on the process for undertaking this driveability assessment. The requirements are provided to support the application of the Common Safety Method for Risk Evaluation and Assessment (CSM RA) to a signalling layout design change, by establishing the adequacy of the presentation of information, by the lineside signalling system, to train drivers.

Uncontrolled when printed

Ref: 18 IA02


2 Initiators of change

2.1 RIS-0713-CCS issue one has been prepared as part of a suite of standards that address safe integration including: Rail Industry Standard on Signalling Layouts and Signal Aspect sequences, (RIS-0703-CCS), Rail Industry Standard on Signal Aspects and Indications (RIS-0758-CCS), Rail Industry Standard for Signal Sighting Assessment Requirements (RIS-0737-CCS) and Rail Industry Standard on Signal Overrun Risk Evaluation and Assessment (RIS-0386-CCS). RIS-0713-CCS issue one can be used in combination with the applications of relevant codes of practice and reference designs, in applying the CSM RA risk acceptance principles to control the hazard of a lineside signalling system that is incompatible with train operations because of poor driveability characteristics.

2.2 The drivability assessment process set out in RIS-0713-CCS issue one is used to establish whether train drivers, in performing their required duties, will be able to reliably act upon the information presented by the lineside signalling system over the range of operational and ambient conditions applicable on the route(s). It contributes to the information that the proposer of the change to a signalling layout will need as part of the overall framework of compatibility assessment and risk assessment that are applied before putting a change into use.

3 Key changes and implications for industry

3.1 The requirements in RIS-0713-CCS issue one address hazards that need to be considered in establishing whether train drivers will be able to reliably act upon the information presented by the lineside signalling system. In addition, requirements are included to address:

a) Signal overrun or a train-on-train collision, where an independent shunt signal is used to present the movement authority (MA) for train movements towards, or along, a passenger line.

b) Excessive signal spacing, where MA information is presented significantly before the time it is needed to make a train driving decision.

c) Variation in signal spacing, where significant variation in the time that cautionary MA information is presented relative to the time that the brakes need to be applied.

3.2 In addition to containing new requirements, the requirements in RIS-0713-CCS issue one also address requirements in GKRT0045 issue five, GERT8071 issue two, and GKRT0075 issue four. The disposition of requirements is set out in Appendices 1 to 4. Appendix 1 identifies new requirements and Appendices 2 to 4 identify the relevant requirements in GKRT0045 issue five, GERT8071 issue two, and GKRT0075 issue four, respectively.

3.3 The RGS GKRT0075 issue four is currently the subject of another standards’ project, and will remain an extant document, and not be withdrawn until the changes identified in the disposition tables in this impact assessment and those associated with the related projects are complete. The implication is that there will be duplication of some of the requirements in GKRT0075 issue four until the redundant RGS can be withdrawn in its entirety. However, as it is the intent that the requirements that are to be retained in a RISs are to be equivalent to those in the RGSs, it is considered that continuing to comply with the RGSs during the transition will not impose additional requirements or associated costs on the industry.

3.4 The RGSs GKRT0045 issue five and GERT8071 issue two have been withdrawn as redundant following the publication of RIS-0713-CCS issue one and RIS-0703-CCS issue one.

3.5 The implications of developing requirements on signalling layout driveability assessments in RIS-0713-CCS issue one are:

a) The incorrect classification of requirements as National Technical Rules (NTRs) is addressed.

b) Those existing requirements which are valid and useful in supporting the industry in the application of the CSM RA to signalling layout designs have been reviewed and updated or retained.

c) Each of the requirements has been validated in terms of its contribution to implementing a signalling layout that is driveable.


Ref: 18 IA02


3.6 The following changes to requirements were made at the consultation stage:

a) A non-material change to the wording of clause 2.1.1 to read ‘The Proposer shall review the proposed change to identify if any of the hazard precursors set out in Table 1 could be introduced by that change.’

b) The inclusion in clause 2.2.2a) to require the rationale for not providing a main signal to be considered in the driveability assessment.

Neither of these changes is considered to have wider implications, with the change to clause 2.2.2 being included for completeness.

4 Predicted impacts

4.1 The withdrawal of requirements from RGSs relating to the signalling layout driveability assessment requirements and their collation in RIS-0713-CCS issue one should not have any wider implications for industry as it is considered that no changes to existing industry practice have been introduced.

4.2 The benefit of RIS-0713-CCS issue one is that it formalises the requirements for a driveability assessment. It brings relevant requirements together into one document and provides supporting information about the hazards each requirement mitigates. This makes it easier for the proposer of a change to identify safety requirements and apply the codes of practice risk acceptance principle alone, or in conjunction with one or other of the risk assessment principles within a CSM RA compliant risk assessment.


Ref: 18 IA02

Appendix 1 New requirements in RIS-0713-CCS issue one


RIS-0713-CCS issue one Comment

Clause No

Requirement

2.1.1 The Proposer shall review the proposed change to identify if any of the hazard precursors set out in Table 1 could be introduced by that change.

Driveability Hazard Precursor

Parameter Identity Description

What information is provided to train drivers

A1 Necessary MA information is not provided by the signalling system

A2 Information provided by the signalling system is not complete

A3 Some information provided by the signalling system is not current

A4 Information provided by the signalling system is not relevant to some trains

A5 Information provided by the signalling system cannot be relied upon

Which signalling displays are used to provide the information

B1 Poor readability

B2 Poor Interpretability

B3 Poor accuracy of the information provided by the signalling system

B4 Inconsistent signal aspects and indications presented along the route

Where information is positioned within the train driver’s field of vision

C1 Unusual or non-compliant signalling asset position relative to corresponding infrastructure features

C2 Inconsistent infrastructure position of one or more signalling assets

When information is provided

D1 Insufficient time for the train driver to comply with the operating requirement

D2 Excessive time for the train driver to comply with the operating requirement

D3 Excessive variation in position of successive lineside signals

D4 Information is provided at inconsistent times

Table 1 Lineside signalling layout driveability hazard precursors

Identifying hazards introduced by the signalling layout enables appropriate measures to be taken to eliminate or mitigate the associated risk.

2.1.2 For each identified driveability hazard precursor, the Proposer shall confirm that the proposed mitigation is sufficient to control the associated risk to an acceptable level.

Managing signalling layout hazards supports the essential requirement safety


Ref: 18 IA02

Appendix 2 Disposition of requirements in GKRT0045 issue five addressed in RIS-0713-CCS issue one


GERT0045 issue five RIS-0713-CCS issue one Comment

Clause No

Requirement Clause

No Requirement

2.2.2.1 Independent position light signals that display the ON aspect using two yellow lights shall only be provided by exception and only as a direct replacement for an existing semaphore yellow shunting disc signal or existing yellow / white position light signal






Table 1 Lineside signalling layout driveability hazard precursors.

The requirement relates to poor driveability and is addressed by clause 3.2.1 of RIS-0758-CCS issue one which permits yellow ‘ON’ aspect. Guidance is also included in clauses G3.2.3 to G3.2.6 of RIS-0758-CCS issue one.

2.2.1 The Proposer shall assess the likelihood of a signal overrun, or a train-on-train collision, where an independent shunt signal is used to present the MA for train movements towards, or along, a passenger line.

3.1.2.4 Before providing a position light signal or semaphore shunting signal to display shunting movement authorities onto or along running lines, the infrastructure manager and relevant railway undertaking(s) shall jointly assess the SPAD risk and collision risk associated with the planned train movements. Factors to be considered shall include (as appropriate): a) Visibility and sighting of the stop signal that defines the end of each

shunting movement authority on the running line. b) The distance to the stop signal that defines the end of each

shunting movement authority on the running line. c) The number and frequency of shunting movements from the signal

that involves train movements onto running lines. d) The proportion of shunting movements from the signal that involve

train movements onto the running line. e) The number and proportion of shunting movements from the signal

into an occupied section on a passenger line.

2.2.1 The Proposer shall assess the likelihood of a signal overrun, or a train-on-train collision, where an independent shunt signal is used to present the MA for train movements towards, or along, a passenger line.

Clause 2.2.2a included at the consultation stage.

2.2.2 This assessment shall consider all of the following: a) The rationale for not providing a main signal b) The frequency of train movements using that signal c) The frequency of train movements from that signal towards, or along, a passenger line d) The frequency of train movements using that signal towards, or along, a passenger line when the

signal section is occupied (permissive shunt) e) The readability of the signal(s) denoting the limit of MA on the passenger line f) The distance to the signal(s) denoting the limit of MA on the passenger line g) The signalling layout at other geographical locations where train drivers might experience similar

train movements h) The operating rules and procedures for using a shunt MA at that location.


Ref: 18 IA02




Clause No

Requirement Clause

No Requirement

4.1.11.1 Within the transition zone between different types of lineside signalling systems, the sequence of displayed signal aspects and indications shall be compatible with:

a) The sequence of aspects leading up to the stop signal at the end of the signalled movement authority that is displayed by the other signalling system, and

b) The permissible speed associated with the movement authority.

2.3.1 and 2.3.2

The Proposer shall assess the impact on driveability of signal aspect sequences where the distance from the first cautionary aspect to the associated stop aspect exceeds the minimum signalling braking distance requirement by 50% or more. This requirement is not applicable where an exemption in Table 2 is applicable.

Criteria Scope of exemption from assessment

Where parallel lines on a multi-tracked route are signalled in the same direction and have different permissible speeds

Signal spacing on the line with the lower permissible speed, if parallel positioning of signals provides a greater benefit

Where lines at a converging junction have different permissible speeds

The signal spacing between the last stop signal on the converging route and the first stop signal beyond the junction

Where signal spacing is optimised for a particular train braking performance

Trains with a braking performance superior to that which the signalling layout is optimised

Where a lower differential permissible speed applies to trains with inferior braking performance

Trains to which the lower differential permissible speed applies

The signal spacing beyond a stop signal protecting the exit from a siding, loop or converging platform line

Trains that start from rest

The signal spacing beyond stop signals where trains start from rest on a through line

The signal spacing approaching a buffer stop at the end of a signalled line

The cautionary aspect sequence associated with the buffer stop

Table 2: Exemptions from the requirement to assess excessive signal spacing

The first cautionary aspect is addressed in clauses 2.7.2.1, 2.7.3.1 and 2.7.4.1 in RIS-0703-CCS-issue one. Clause G3.1.4 in RIS-0713-CCS issue one provides guidance on what is to be considered in a driveability assessment. The driveability assessment addresses the physical attributes of the railway and the operational context on the signalled lines, together with those factors which impact on train driving.

5.1.2.9 The same alphanumeric route indication shall not be displayed by separate signals for movements towards different destinations at any one locality.






Table 1 Lineside signalling layout driveability hazard precursors.

Establishing that the information provided to the train driver is unambiguous is undertaken as part of the drivability assessment consideration of the ‘poor interpretability’ hazard precursor identified under B2 in Table 1 of RIS-0713-CCS issue one.


Ref: 18 IA02




Clause No

Requirement Clause

No Requirement

5.2.2.1 The signalling system shall only display a standard 3- or 4-aspect sequence and an unrestricted aspect at the junction signal when both of the following apply: a) The difference between the permissible speeds of the straight

ahead and diverging routes through, and immediately beyond, the junction is 10 mph or less, and

b) No safety hazard would arise if the train is wrongly routed at the junction (for example, gauge or traction supply incompatibility





B4 Inconsistent signal aspects and indications presented along the route


Also addressed in guidance G 3.8.1, G 3.8.2 and G 3.8.4 in RIS-0703-CCS issue one’

5.2.3.1 Junction method 2 shall only be used where all of the following apply: a) The speed reduction to the permissible speed at the point of

divergence falls within the ranges set out in Table 2. b) The divergence is not into a terminal line. c) There is no operational requirement to reduce the speed of the

train at the junction.

Also addressed in guidance G 3.9.1.6 and G 3.9.1.9 in RIS-0703-CCS issue one.

5.2.3.6 a)-d) A flashing aspect sequence shall only be displayed when the approaching train is detected to be in a position that is compatible with the required reading time of the junction distant signal that displays the flashing single yellow aspect and one of the following applies: a) The first signal beyond the diverging junction is a controlled stop

signal that is either one of the following: i) Displaying an OFF aspect. ii) Displaying an ON aspect and a forward route is set. iii) Displaying an ON aspect at the end of a loop line or platform

line where all trains are expected to stop. b) The first signal beyond the diverging junction is an automatic signal. c) The first signal beyond the diverging junction is an isolated distant

signal. d) The train protection system is configured to mitigate the SPAD risk

at the first stop signal beyond the diverging junction

Guidance on flashing aspects is given in G 3.9.1.7, G 3.9.1.11 and G 3.9.1.12 in RIS-0703-CCS issue one.

5.2.5.1 By exception, the signalling system shall only be configured to display the normal 4-aspect sequence leading up to a free single yellow at the junction signal, where all of the following apply: a) It is not appropriate to use junction method 1 or junction method 2. b) All trains that operate over the route have a consistent braking

characteristic (see GKRT0075). c) The signalling braking distances (see GKRT0075) is compatible with

the requirements for 4-aspect signalling between: i) The junction distant signal that displays the double yellow aspect

and the junction signal, and ii) The junction signal and the first signals on all routes beyond the

junction. d) The braking performance of the trains shall be compatible with:

i) The distance between the junction distant signal that displays the double yellow aspect and the point of divergence, and

Clause 3.10.1 of RIS-0703-CCS issue one sets out requirements for junction aspect sequences where the main junction signal is approach controlled from a 4-aspect single yellow caution which is preceded by a 4-aspect first caution. Guidance on free aspect yellow is given in G 3.10.1.8 in RIS-0703-CCS issue one


Ref: 18 IA02




Clause No

Requirement Clause

No Requirement

ii) The required speed reduction to the permissible speed at the point of divergence.

e) The highest permissible speed for any route at the junction is 60 mph or less.

f) The difference in speed for the divergence is greater than 10 mph and not more than 30 mph.

5.2.6.1 By exception, the signalling system shall be configured to display a

splitting distant aspect sequence leading to an unrestricted aspect at the junction signal.

n/a n/a Clause 3.11.1 of RIS-0703-CCS issue one sets out requirements for junction aspect sequences where an unrestricted main junction signal is preceded by a splitting distant proceed aspect, with guidance in G3.11.1.4 to G3.11.1.7.

6.1.1.2 Where reduced capacity bi-directional signalling facilities are provided: a) Consecutive contraflow direction stop signals shall be spaced no

more than 10 miles (16 km) apart, and

b) Contraflow direction stop signals and distant signals shall be positioned so that there is a parallel signal provided for movements in the same direction on adjacent line(s).

The Proposer shall review the proposed change to identify if any of the hazard precursors set out in Table 1 could be introduced by that change.



When information is provided

D2 Excessive time for the train driver to comply with the operating requirement

D3 Excessive variation in position of successive lineside signals

D4 Information is provided at inconsistent times





B1 Poor readability


Establishing that the timing that the information is provided to the train driver is appropriate is undertaken as part of the drivability assessment consideration of the hazard precursor identified under D2, D3 and D4 in Table 1 of RIS-0713-CCS issue one. Establishing that the information provided to the train driver is unambiguous is undertaken as part of the drivability assessment consideration of the hazard precursor identified under B2 in Table 1 of RIS-0713-CCS issue one. Guidance on parallel positioning of signals is given in clauses G2.2.1.20, G2.2.1.23 and G2.2.1.24 of RIS-0703-CCS issue one


Ref: 18 IA02

Appendix 3 Disposition of requirements in GERT8071 issue two addressed in RIS-0713-CCS issue one


GERT8071 issue two RIS-0713-CCS issue one Comment

Clause No

Requirement Clause

No Requirement

2.1.1.2 The assessment of compatibility shall check that the provision of PoSA facilities is compatible with the arrangements




What information is provided to train drivers

A1 Necessary MA information is not provided by the signalling system


Establishing that the lineside signalling system is compatible with all reasonably foreseen train operations that require a signalled movement authority is undertaken as part of the drivability assessment consideration of hazard precursor identified under A1 in Table 1 of RIS-0713-CCS issue one.


Ref: 18 IA02

Appendix 4 Disposition of requirements in GKRT0075 issue four addressed in RIS-0713-CCS issue one


GKRT0075 issue four RIS-0713-CCS issue one Comment

Clause No

Requirement Clause

No Requirement

2.1.3a The assessment of compatibility shall check that the actual signalling braking distance is compatible with the SPAD risk mitigation measures that will be put in place by the railway undertakings, where any of the following apply:

a) There is more than 50% excess signalling braking distance, except where an exemption applies (see Table 1).

Situation

Scope of compatibility check where actual signal spacing exceeds the

minimum signalling braking distance by more than 50%

a Where signals control movements in the same direction on parallel lines that have different permissible speeds, and signals are positioned adjacent to each other to minimise the risk of driver misread or disregard

The compatibility check is only required for signalling braking distances on the higher speed line. Signal braking distances on the lower speed line are exempt from the compatibility check

b Where trains join a higher speed line at a converging junction from a lower speed line or start from a siding, loop or another platform line

The compatibility check is only required for signalling braking distances on the higher speed line. Signal braking distances for train movements from the lower speed line are exempt from the compatibility check

c Where trains start from a platform on a through line

The compatibility check is only required for signalling braking distances associated with non-stopping trains. Signal braking distances for train movements that start from rest are exempt from the compatibility check

d Where the signal spacing is designed using particular signalling braking distance data (for example, Appendix A for a mixed traffic line)

The compatibility check is only required for signalling braking distances associated with the appendix to which the line is signalled

e Where the signal spacing is designed to Appendices B or C, and a differential speed restriction is applied to enable traffic with an inferior braking characteristic to operate

The compatibility check is only required for signalling braking distances associated with the appendix to which the line is signalled

f At the approach to buffer stops at terminal stations or at bay platforms

The compatibility check does not apply to the spacing distance between the approach signals and the buffer stops

Table 1 Exemptions from compatibility check

2.3.1 and 2.3.2

The Proposer shall assess the impact on driveability of signal aspect sequences where the distance from the first cautionary aspect to the associated stop aspect exceeds the minimum signalling braking distance requirement by 50% or more. This requirement is not applicable where an exemption in Table 2 is applicable.

Criteria Scope of exemption from

assessment

Where parallel lines on a multi-tracked route are signalled in the same direction and have different permissible speeds

Signal spacing on the line with the lower permissible speed, if parallel positioning of signals provides a greater benefit

Where lines at a converging junction have different permissible speeds

The signal spacing between the last stop signal on the converging route and the first stop signal beyond the junction

Where signal spacing is optimised for a particular train braking performance

Trains with a braking performance superior to that which the signalling layout is optimised

Where a lower differential permissible speed applies to trains with inferior braking performance

Trains to which the lower differential permissible speed applies

The signal spacing beyond a stop signal protecting the exit from a siding, loop or converging platform line

Trains that start from rest

The signal spacing beyond stop signals where trains start from rest on a through line

The signal spacing approaching a buffer stop at the end of a signalled line

The cautionary aspect sequence associated with the buffer stop

Table 2: Exemptions from the requirement to assess excessive signal spacing

The aim of this assessment is to confirm that train drivers will be able to manage any MA information that is presented significantly before the time it is needed to make a train driving decision. The exemptions in Table 2 represent circumstances where excessive signal spacing results either from alternative signalling layout design solution that would improve driveability or the operational context. In these cases, it is unlikely that repositioning signals to reduce signal spacing would provide an overall benefit.


Ref: 18 IA02

Appendix 4 Disposition of requirements in GKRT0075 issue four addressed in RIS-0713-CCS issue one


GKRT0075 issue four RIS-0713-CCS issue one Comment

Clause No

Requirement Clause

No Requirement

2.1.3b The assessment of compatibility shall check that the actual signalling braking distance is compatible with the SPAD risk mitigation measures that will be put in place by the railway undertakings, where any of the following apply:

a) …….

b) A variation in excess signalling braking distances means that the distance between the signals displaying the first cautionary aspect and the stop aspect is reduced by 34% or more, compared with the excess signalling braking distance for the preceding sequence of signals on the same line.

c) ……

2.4.1 The Proposer shall assess the impact on driveability where excessive signal spacing at consecutive signals on the same line reduces by 34% or more.

The aim of the assessment is to confirm that the train driver can manage the significant variation in the time that cautionary MA information is presented relative to the time that the brakes need to be applied.

2.1.3c The assessment of compatibility shall check that the actual signalling braking distance is compatible with the SPAD risk mitigation measures that will be put in place by the railway undertakings, where any of the following apply:

a) ……

b) ……

c) In four-aspect signalling areas, where the distance between the signals displaying the single yellow aspect and the red aspect is less than one third of the distance between the signals displaying the double yellow aspect and the red aspect.





B3 Poor accuracy of the information provided by the signalling system

Where information is positioned within the train driver’s field of vision

C2 Inconsistent infrastructure position of one or more signalling assets


Clause 2.8.3.1c of RIS-0703-CCS issue sets out the conditions for when the 4-aspect single yellow caution aspect is to be presented; with guidance provided in clauses G.2.8.1.3.13, 2.8.3.29 and 2.8.3.30.


Ref: 18 IA02

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Impact assessment for changes to a Railway Group … IA02.pdf · RSSB impact assessment: RIS-0713-CCS Issue: Final Page 1 of 11 Impact assessment for changes to a Railway Group