Analysis of past derailments
Information from data bases, investigation reports and surveys
Terje Andersen
06 May 2011
Purpose of Accident Analysis
 Qualitative Analysis:
- To provide information on observed derailment causes.
- To identify those causes that are “single point failures” and that in most cases can be
considered direct derailment causes (axle failure, wheel failure etc).
- To identify those causes that are “contributory” and can be considered to make a derailment
more likely (by eroding the safety margin, e.g. operational issues, wagon skew loading etc).
- To identify the range of possible consequences following a derailment.
- And therefore to provide the structure for a risk model.
 Quantitative Analysis:
- To provide statistical analysis of the relative frequency of individual / combinations of failures
leading to a derailment.
- To provide statistical analysis of the relative likelihood (probability) of consequences following
a derailment.
- And therefore to provide the data for a risk model.
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Depth and Breadth of Accident Analysis
 Accident Investigation reports from National Investigation Bodies (NIB):
- The percentage of derailments investigated by the National Investigation Bodies varies significantly from
country to country.
- Some countries investigate a very high number of railway accidents and go far beyond what is mandatory.
 Annual reports of National Investigation bodies:
- For countries reporting only mandatory accidents, the annual reports of the NIBs can give some
information on “non-investigated” accidents.
 ERADIS database entries:
- Supported by the accident investigation report where required to provide additional information.
 Previous Agency survey
- Significant amounts of information has also received from the Agency for the 2008 study of the Derailment
Detection Device.
 Other information sources.
 In total we have about 700 freight train derailment accidents (although some of these are
marshalling / freight yard derailments) in our database, covering 23 countries.
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Accident Analysis Summary
Accident Causes Breakdown
1%
25%
36%
37%
Infrastructure
Rolling stock
Operational failure
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Others (environment etc)
Accident Analysis Findings - Infrastructure
 Track geometry defects
account ~ 70% of
infrastructure related
derailments, and ~ 30% of all
derailments
80%
70%
60%
50%
40%
- Excessive track twist 27%
- Excessive track gauge 19%
30%
 Main controls are inspection,
maintenance, adherence to
standards etc.
10%
20%
0%
Substructure
(subsidence, bridge
failure etc)
Superstructure (rail
ruptures, fastening,
switch etc)
Track geometry (twist,
width, height, cyclic
tops, buckles etc)
Other
 Occur more often in station at
turnouts or signals
 However, in many cases the defect was known about.
 Derailments due to sun curve (heat buckle) are more common in Nordic countries.
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Accident Analysis Findings – Rolling Stock
 Axle ruptures and wheel
failures account ~ 57% of
rolling stock related
derailments, and ~ 20% of
all derailments.
- Bearing failure -> hot axle
box -> axle journal rupture
most frequent RS caused
derailment scenario
 Main wagon controls are
inspection, maintenance,
adherence to standards.
45%
40%
35%
30%
25%
20%
15%
10%
5%
0%
Failure of axles
(ruptures)
Failure of wheels
(composite or
monoblock)
Bogie Suspension and
Structure (spring,
wagon frame etc)
Others and
Unknown
- Infrastructure detection
devices
 However a number of trains derailed due to a HAB had recently passed a HABD.
 HAB failures are less common in some countries than others.
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Accident Analysis Findings – Operations
 Incorrect / improper
loading account ~ 25% of
derailments caused by
operational failures, and ~
10% of all derailments.
 Main controls are:
-
operational rules
inspection
functional tests
training & competent staff
30%
25%
20%
15%
10%
5%
0%
Train formation
and testing (train
composition,
brake test not
performed etc)
Train loading
(overload, skew
loading etc)
Mishandling of
train (overspeed
etc)
Turnouts (point
movement,
incorrect setting
etc)
Others (objects
under train, etc)
 Main failings are human errors / acts of omission / acts of commission.
 Skew loading often works in combination with track geometry defects leading to
derailments.
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Combination of causes often necessary to cause derailment
 Very often the derailment is caused by a combination of several contributory
causes e.g.:
- Combination of faults of infrastructure and rolling stock
- Combination of a Rolling stock or Infrastructure fault and unfortunate train
handling/operation
 Typical examples are:
- Low train speed and sudden train braking action combined with:
- Track twist, narrow curve with high cant
- Track twist, wagon with very long wheel base
- Track twist and twisted or skew loaded wagons
- Track geometry fault and strong compression forces in train due to unfortunate
train composition or less than optimal train handling by the driver
 Existing measures are often directed towards control of these common
causes of freight train derailment, with varying degrees of success.
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Some causes in detail – Rolling Stock
 The event sequence bearing failure >
hot axle box > sheared axle journal is
the most common derailment cause
accounting for about 40% of rolling
stock derailments.
 There appear to be geographic
differences between countries.
 Most, but not all, countries have hot
axle box detectors trackside to provide
warning:
- But present use of HAB-detectors is far from 100
% effective
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Excessive track twist most important infrastructure failure cause
 Derailments occur under presumably safe
conditions
 Upper figure shows track twist limitations for
curves R > 420 m
- UK has more lenient requirements
- > higher proportion of track twist derailments
- Derailment has occurred within allowable limit
- Neulengbach (AT)
 Lower figure shows track twist limitations for
curves R < 420 m
- Derailment has occurred within allowable limit
- Fetsund (No) & Rosenbach (AT)
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