A distracted driver and excessive speed caused a KiwiRail freight train to derail in March last year.
The Transport Accident Investigation Commission (TAIC) found that the freight train had exceeded the maximum permissible track speed when exiting the crossing loop.
The TAIC report said this was due to the driver becoming distracted and the downhill gradient of the track allowing the train to accelerate to above the maximum permissible line speed.
The incident occurred on March 29, 2019 when the three rear wagons of the KiwiRail freight train derailed as the train exited a crossing loop at Clinton on the way from Invercargill to Dunedin, New Zealand.
Two of the three derailed wagons overturned onto their sides, causing damage to the wagons, track, and a signal.
“A train driver can become distracted even when carrying out tasks specific to their role which, if poorly timed, can have unintended consequences,” the commission said in the investigation report.
The TAIC reported in its investigation findings that a phenomenon known as dynamic interaction was very likely the cause of the derailment.
Dynamic interaction occurred where the excessive speed combined with the track geometry at the point of derailment and the centre of gravity of the fully loaded coal wagons caused the wagon to oscillate from side to side. One or more wheels then lifted and climbed the rail, resulting in derailment.
The wagon condition and loading were found to be within KiwiRail’s maximum permissible limits, the TAIC found.
A similar derailment occurred at the Clinton crossing loop in 2016, which was not investigated by the TAIC.
“At that time KiwiRail took a number of safety actions after the incident, including speed monitoring and track repair,” the TAIC stated.
“However, a procedural control measure to ensure that loaded trains did not use the crossing loop was not adopted.”
The TAIC acknowledged in the investigation report that KiwiRail has taken a number of safety actions that addressed the issues raised in this report and that therefore no new recommendations needed to be made.
“To avoid repeat accidents and incidents it is important to learn from previous incidents,” the TAIC stated.
“This requires a focus on implementing corrective action in accordance with the hierarchy of controls.
“However, when procedural control measures have been identified they should be implemented, checked and monitored properly to ensure the desired results are achieved.”
Siva Sivapakkiam, KiwiRail executive general manager operations told Rail Express that the derailment of three wagons last year at Clinton was a serious incident, and KiwiRail has treated it as such.
“As the TAIC report notes, we have already made a change to our operating procedures to ensure that fully laden coal trains heading to Dunedin use only the main line when passing through Clinton,” she said.
Sivapakkiam said this avoids fully laden trains having to proceed through the crossing loop points, and it also means that the speed of empty Invercargill bound trains entering the loop is reduced by the uphill geometry of the track.
“Drivers have again been briefed on the need to ensure that the whole length of the train remains within the appropriate speed limit when entering or exiting crossing loops,” she said.
“We have instituted a non-technical skills training programme which provides staff with the knowledge to identify and manage distraction.
“In addition a redesign of the points configuration at Clinton is planned. We note that TAIC did not make any new recommendations for further action.”