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Track twist from an embankment losing ballast support

Willesden High Level Junction, north-west London · 6 May 2019

A degrading earth embankment and lost ballast support produced a significant track twist on a tight curve. Information about the earthwork and the track sat with separate teams.

What happened

At around 21:30 on 6 May 2019, a single empty two-axle wagon in a freight train derailed on a curve approaching Willesden High Level Junction.

The wagon re-railed as it passed over the junction. No one was hurt, but a derailment like this can foul lines open to passenger trains.

What the investigation found

  • The leading wheel had too little load, so its flange climbed the rail, because the wagon met a significant track twist while carrying an uneven wheel load.
  • The twist developed rapidly on an earth embankment that had been monitored since October 2016, showed seasonal movement and was in poor condition, with ballast support lost from under the sleepers.
  • Inspection, maintenance and mitigation measures did not detect the risk. Separate track and earthworks teams not sharing information was identified as a possible underlying factor.
  • The wagon had a diagonal wheel load imbalance that routine maintenance had not detected.

Timeline

  1. From Oct 2016Embankment monitored; progressive seasonal movement recorded.
  2. Before May 2019Ballast support lost under sleepers; track twist develops quickly on the curve.
  3. 6 May 2019, ~21:30Empty wagon derails on the curve and re-rails at the junction.
  4. 25 Aug 2020RAIB publishes report 07/2020 with four recommendations.

Where Ralliyo fits

The evidence below is the kind Ralliyo records and keeps together. It shows how the capabilities map to the findings, not a claim about what would have happened.

One record for track and earthworksBallast contamination · Unusual trackside conditionBallast loss, voids and embankment signs recorded against the section sit next to track observations, so neither team sees only half the picture.
Documents with contextEarthwork monitoring reports can be attached to the network and cited by Copilot alongside inspection findings.
PrioritisationSections with worsening ballast observations move up the attention list with the reasons shown.
Limits. Track twist is a geometry measurement. Ralliyo does not replace track recording or earthwork monitoring; it brings their findings together with visual inspection evidence.

RAIB recommendations

  1. Clarify the use and limitations of track geometry recording data for understanding track bed and earthwork condition.
  2. Introduce measures to mitigate risks from known defects in supporting earthworks.
  3. A further recommendation to Network Rail (see the full report).
  4. Improve maintenance of this wagon type (to DB Cargo).