Analysis of past derailments

1. Analysis of past derailments Information from data bases, investigation reports and surveys

2. 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.

3. 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.

4. Accident Analysis Summary

5. Accident Analysis Findings - Infrastructure • Track geometry defects account ~ 70% of infrastructure related derailments, and ~ 30% of all derailments • Excessive track twist 27% • Excessive track gauge 19% • Main controls are inspection, maintenance, adherence to standards etc. • 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.

6. 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. • Infrastructure detection devices 45% 40% 35% 30% 25% 20% 15% 10% 5% 0% Failure of axles Failure of wheels Bogie Suspension and Others and Unknown (ruptures) (composite or Structure (spring, monoblock) wagon frame etc) • 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.

7. 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 • Main failings are human errors / acts of omission / acts of commission. • Skew loading often works in combination with track geometry defects leading to derailments.

8. 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.

9. 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

10. 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)