The ATSB is highlighting the importance of maintaining track condition on small-radius curves to reduce the risk of flange-climb derailment.
The ATSB’s investigation into the derailment of a Metro Trains Melbourne (MTM) passenger train near Rushall Station in Melbourne on 6 February 2016 has been released. The investigation was conducted by the Victorian Office of the Chief Investigator, Transport Safety, on behalf of the ATSB under the Transport Safety Investigation Act 2003.
At about 1650, the passenger train was negotiating the most severe mainline curve on the metro network when the lead bogie of the second car derailed.
The ATSB found that the leading right-hand wheel of the second car climbed the outside rail of the small-radius curve. The main factors contributing to the derailment were the geometry of a rail joint and the high coefficient of friction between wheel and rail. The train was being operated within the speed limit for this curve and the manner of its operation did not contribute to the derailment.
For small-radius curves, the effective management of track condition is critical to reduce the risk of flange-climb derailment.
The derailment at this point on the curve was triggered by a lateral angular discontinuity at a mechanical rail joint, resulting in a localised increase in the wheel-to-rail lateral force. The network’s track geometry standard did not preclude the presence of such a discontinuity.
It was also found that the train’s wheel flanges and the rail’s gauge-face had low levels of lubrication. The performance of rail lubricators on the metropolitan network had diminished prior to the derailment, leading to a deficiency in lubrication on the network.
While not mandated by MTM, a check rail on this small-radius curve (installed adjacent to the inner rail) would have provided an additional defence against flange climb and derailment.
A number of other safety factors were identified that were not directly causal to this incident. They included a high tolerance on allowable track geometry deviations at low-speed mainline locations, a failure to address a wide-gauge defect on this curve, and the ineffective locating of some rail lubricators within the network.
To reduce the risk of future derailments on similar curves, MTM has undertaken a range of actions including significant changes to the management of track condition and faults and the installation of new electronic lubricators.
Read the full investigation report RO-2016-002: Derailment of MTM train TD1064 near Rushall Station, Melbourne, Victoria, on 6 February 2016Last update 08 June 2018