16 November 2006
The TSB Establishes a Relationship Between Secondary Main-Line Derailments and Bulk Tonnage Traffic
The Transportation Safety Board of Canada (TSB) today released
its Safety Issues Investigation Report SII R05-01 that establishes a relationship between
secondary main-line derailments and bulk tonnage traffic.
In the winter of 2003-2004, a series of train derailments on secondary main lines in western Canada involving broken
rails prompted the TSB to initiate a safety issues investigation (SII). To develop an understanding of the factors underlying these
occurrences, the investigation examined the commonalities among these occurrences, reviewed relevant TSB data, and used data provided
by the railways to test a specific hypothesis - that bulk tonnage traffic, independent of cumulative tonnage, is associated with
increased derailment risk due to rail defects.
The SII reveals that a statistically significant relationship exists between the incidence of rail defects and the level of bulk
tonnage traffic. Where rail weight is less than 130 pounds, increased bulk unit train tonnage significantly increases rail defects,
resulting in a higher risk of broken rail derailments. Risks related to the problems in balancing track maintenance and degradation to
the comprehensiveness of the Railway Track Safety Rules and to deficiencies in rail inspection capabilities and maintenance practices
were identified.
The quantitative analysis was conducted only on Canadian Pacific Railway (CPR) subdivision data because an insufficient number of
Canadian National (CN) subdivisions met the specific selection criteria to furnish a sample of sufficient size to perform a similar
analysis.
An SII reviews multiple occurrences that the Board suspects have similar underlying factors. The overall significance of secondary
main-line derailments and identification of the relationship to bulk tonnage traffic would have been less likely through
individual occurrence investigations.
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