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Driver injured in tip-over of logging truck and trailer

Date of incident: August 2013
Notice of incident number: 2013108440067
Employer: Logging company

Incident Summary

A truck with its loaded four-axle log trailer was approaching a bridge. While nearing the end of the on-ramp, the truck and log trailer tipped onto the driver's side, spilling the logs onto the road and median. The truck and log trailer were damaged, and the driver was injured. The same log trailer had been involved in a similar incident about three months earlier, also on an on-ramp onto a bridge.

Investigation conclusions


  • Mechanical deficiencies caused tip-over of loaded log truck and trailers: The truck and loaded log trailers were travelling on a 90-metre-radius right-hand turn, approaching the bridge deck, when they tipped onto the driver's side, spilling the logs. All the mechanical deficiencies of both the log trailers and the truck's fifth wheel, taken together, allowed the centre of gravity to shift significantly, and the speed of the truck and trailers created the forces that caused the tip-over.

Underlying factors

  • Worn bunk components: Components of the rear bunk, such as the "cup and saucer," were worn past the manufacturer's specifications. The loose rear bunk resulted in the load shifting abruptly to the driver's side as the truck made the right-hand turn.
  • Warped upper plate and fifth wheel: The warped upper plate at the front of the log trailer and the warped fifth wheel on the truck resulted in insufficient contact between these components. During the right-hand turn, this extra space permitted the load on the trailer to shift more to the driver's side than normal. This caused the weight of the logs to shift the centre of gravity to the driver's side of the trailer unit.
  • Under-inflated log trailer tires: The 16 trailer tires were intentionally under-inflated by 33 percent, which resulted in decreased vehicle stability and a lower safe-cornering speed. The under-inflated tires also contributed to shifting the centre of gravity more towards the driver's side of the trailers during the right-hand turn.

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Publication Date: Aug 2013 Asset type: Incident Investigation Report Summary NI number: 2013108440067