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Final Report

Summary

What happened

At about 1650 on 6 February 2016, metropolitan passenger train TD1064 was travelling towards Melbourne between Merri and Rushall Railway Stations when it derailed one bogie on a small-radius curve. There was one minor injury reported.

The derailed car was foul of the adjacent track and there was the potential for more serious consequences had a train from the opposite direction been passing at the time.

What the ATSB found

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 high coefficient of friction between wheel and rail and the geometry of a rail joint. The train was being operated within the speed limit for this curve and the manner of its operation did not contribute to the derailment.

It was 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. This was probably the result of a decline in lubricator maintenance. Rail lubricator maintenance was being transferred from contractors to Metro Trains Melbourne (MTM) staff and this transition was not adequately managed.

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.

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 network standard to potentially address derailment risk at higher-risk locations was under consideration at the time of this derailment.

A number of other safety factors were identified that were not directly causal to this incident. They included the ineffective locating of some rail lubricators within the network, a high tolerance on allowable track geometry deviations at this and similar low-speed mainline locations, and a failure to address a wide-gauge defect on this curve.

What's been done as a result

MTM have undertaken a range of actions including the wide-spread installation of new electronic lubricators and significant changes to the management of track condition and faults. These actions, when taken in concert, are expected to reduce the risk of derailment on small-radius curves.

Safety message

The potential for flange-climb derailment on small-radius curves is sensitive to track condition and lubrication between wheel and rail gauge-face. It is therefore important to maintain lubrication across the network and address reductions in performance flagged by unusual wheel wear or evidence of metal loss at the wheel-rail interface.

Occurrence

Context

Safety analysis

Findings

Safety issues and actions

Sources and submissions

 
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