The car was stationary at the level crossing because of a "complicated roadworks operation" in the area, chief investigator of accidents Harald Hendel said.
"The car had moved off from a stop/go sign, drove through the roadworks area and then on to the level crossing.
"This was despite the level crossing warning bells and lights that had been automatically activated by the approaching train.
"It's likely the traffic controller's 'go' signal led the car driver to believe they were cleared to drive through the entire roadworks area, which included the level crossing."
Hendel said a contractor's car with a flashing amber light was parked next to the crossing's flashing warning lights, adding to the confusion.
He said a traffic management plan approved for the roadworks had the safety of road workers in mind, but "overlooked the need to keep road users safe from trains".
The TAIC report also pointed to another major failing by the roadworks contractor: it did not ask KiwiRail for permission to work in the rail corridor, so the rail operator was unaware of the work.
"This meant there was no rail safety oversight by KiwiRail and no special measures for trains on that section of track," said Hendel.
TAIC recommended Waka Kotahi check that agencies approving traffic management plans on state highways are doing so correctly and that the Secretary for Local Government (DIA) ensure that contractors consult rail access providers and meet any additional safety requirements where road and rail meet.
