Safety related applications of GNSS: lessons learned, way forward Martyn Thomas Rail Safety and Stan

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Safety related applications of GNSS lessons
learned, way forward Martyn ThomasRail Safety
and Standards Board(RSSB)Railways and GNSS
London 8 Feb2005
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Safety and Transport

• GNSS is applied widely to
• Road
• Aviation
• Maritime
• and is finding acceptance in the
• Railways
• But safety applications are still developing

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Some railway applications
Position and speed related functions Respect of
signals Respect of speed profile Level crossing
controls Track worker safety Door controls Train
presence Train length Asset and maintenance
information
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Safety issues
Responsibility Accountability Knowledge Self-reli
ance?
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Safety in railways

• Safety in traffic control
• Route integrity
• Train location
• Train speed
• Safety for trackside workers
• Safety at level crossings

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Traffic Control

• Movement authority cannot be less restrictive
  than intended.
• Dependence on a system requires that
  failures/errors do not permit unauthorised
  movement
• This is assured by either
• Intrinsic physical properties
• Positive validation

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Measure of Safety

• In railways it is undetected failures that are
  a threat to safety.
• Safety is best treated in a statistical manner.
• Rate of undetected failures.
• System Integrity Levels (SILs) categorise ranges
  of undetected failure rates

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Comparison with other modes
Rail Consequences reveal within a few
minutes. Failures stop operations. Aviation
Role of continuity over short periods Maritime
Consequences slow to reveal Road Little
formalised dependency on systems
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Effect of GNSS errors on railway

• Train is behind measured location
• Train is ahead of measured location
• Train running faster than measured
• Train running slower than measured

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Hazards and Risk
Hazards are everywhere! Risk is associated with
each hazard ( frequency x consequence) Safety
performance required determines the risks to be
addressed.
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Hazards and GNSS

• The hazards of GNSS have to be identified.
• Before use in safety applications the hazards
  have to be understood and the associated risk
  identified.
• Applies to Space, Augmentation, Ground and
  Receiver segments
• Quantification preferable.

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The Difficulties
GNSS-based performance is statistical Railways
are 24/7/365 (at least in principle) System
accuracy and tolerances have to be fit for
continuous service Satellite obscuration is a
fact of railway life.
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The Benefits

• Current technology in use is not brilliant
• GNSS availability is high
• GNSS and its hybridisation and its augmentation
  offer great diversity
• The functional performance is good
• The technologies are progressively more cost
  effective

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Some GNSS Hazards
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Data Fusion

• Data fusion is part of the solution.
• Use a range of sensors
• Data fusion hazards must be assessed.

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Secondary Channel Processing

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Future Work

• To demonstrate that the risks associated with
  GNSS and data fusion are understood and
  controlled.

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• THANKYOU