Accident investigators have found KiwiRail did not act on prior warnings of a wheel-bearing failure in time to stop a freight train coming off the tracks.
The train was on its way from Tauranga to Auckland in September 2013 when a wheel bearing on the 20th wagon failed, and that wagon and two others derailed.
The contents of one of them spilled onto State Highway 1 and there were initial fears hazardous material was on board.
A crane had to be used to remove the containers.
Transport Accident Investigation Commission found KiwiRail had put a monitoring system on the tracks to detect any signs of wheel-bearing failure.
Although the system detected an impending problem, it was not acted on because the system was not fully resourced or implemented, the report found.
"Under the procedures adopted since this derailment there is a greater likelihood that the wagon would have been taken out of service for inspection and remedial work before the failure occurred, thus preventing this derailment," it said.