A locomotive derailed after its driver missed signals to slow down and travelled through a track crossing 46km/h faster than the allowable speed.
A report into the incident said the train was returning from Waitakere to the Otahuhu yard in the early hours of March 2, 2014.
Train 5153, a DC class diesel-electric locomotive hauling four empty passenger carriages, was carrying a driver and a train manager in the rear carriage.
At Westfield, the driver failed to slow for a 25km/h crossover, which would take the train from one parallel track to another.
The locomotive entered the crossover at 71km/h, derailed and rolled over.
A Transport Accident Investigation Commission (TAIC) report into the incident said the train had passed three trackside signals and one route indicator alerting the driver to slow for the crossover ahead.
The driver made a full-service brake moments after passing the third signal, too late to slow the 210 tonne train in time.
The locomotive rolled and slid for 94m, while the following two carriages derailed but remained upright. The driver and train manager suffered minor injuries.
Significant damage was caused to the train and track.
The driver said he had never been directed over the Westfield crossover in his 20 months of driving.
The fact the incident occurred in the early morning when performance is at its lowest, and the driver was nearing the end of a nine hour shift, meant he either didn't look at, or didn't comprehend the significance of the signals, the report said.
A new system is being rolled out in Auckland's electric trains which would allow them to be automatically slowed if the driver bypasses signals.
The system wasn't retrofitted to trains due to be phased out this year because of the $11 million cost.
TAIC said Kiwirail's policy for communicating with drivers over changes in their route was unclear.
Since the incident Kiwirail said it was working on a project to improve driver situational awareness and decision-making.
Transdev has introduced a risk assessment project and extra training for drivers.