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Requirments for safe design
Hi all, I found this question in EXAMPLE IRSE EXAMINATION PAPER: MODULE C.

c) What information must be provided when signalling a layout in order that operators can assess whether it meets their requirements, and for designers to be able to generate detailed safe designs?

Can anyone confirm if this answer is accurate or not ?

 2.3 Design Objectives: Design for Safety, Performance And Economy.
When performing the task of Signalling the Layout, the engineer must keep these different
considerations in mind; examples how each of these factors influences the design are listed below.

Safety considerations:

• Provision of a locked, proved wheel path for each train,
• Protection to authorised train movements from unauthorised moves elsewhere,
• Signals positioned to protect conflicts adequately,
• Junction layout design (avoidance of single-lead junctions, minimise conflict length,
converging sideswipe preferable to head-on collision) and signalling of the divergence,
• Minimise length of any “bang road” movements in the direction contrary to predominant
traffic flow,
• Braking distance warning for any signal at danger (aspect sequences and transitions),
• Consistency of signal spacing,
• Optimisation of signal sighting distances,
• Awareness of SPAD-traps (ideally avoid, otherwise mitigate),
• Awareness of environment at signal positions (ideally avoid, otherwise mitigate)
• Provision of train protection to provide back-up to pure reliance on the driver in to control
appropriately the speed of their train,
• Determination of suitable overlap length and direction to provide safest possible overrun.

Performance considerations:

• Maximum speed limits for all categories of train for plain line and junctions,
• Maximum line capacity by minimising headway time between trains,
• Suitable for maximum train lengths specified,
• Ability to perform the movements needed in order to operate the train service (permissive
movements to allow joining of trains, locomotive running around trains, shunting, propelling
movements, ECS movements to depot etc.)
• Promote efficiency in operational use, ease / simplicity of communication etc.,
• Maximum flexibility in use of layout (parallel moves, permissive moves
• Maximum resilience in event of failure:
-­ ability to limit effect by “work-around”),
-­ Provision of reversible signalling on double track lines,
-­ Minimise number failures by minimum equipment count.

Cost considerations:

• Only provide the functionality actually really needed,
• Minimise quantities of equipment utilised,
• Simplest layout to avoid interlocking complexity,
• Utilisation of standard solutions,
• Utilisation of appropriate technology to meet the operational and technical requirements.

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