A rail supervisor who let a passenger train come within 72 metres of workers replacing sleepers on a railway bridge later tested positive for methamphetamine, an investigation says.
The incident occurred on the main trunk line near Taumarunui in December 2015, and has been detailed in a Transport Accident Investigation Commission report.
During the morning of the incident, four freight trains passed through the work site without incident.
But the site's rail protection officer authorised a passenger train to pass through over the radio and forgot to clear the workers from the bridge.
The alert train driver stopped his train 72m short of the men. There was no collision and no one was injured.
The commission said the supervisor's positive post-incident test result for methamphetamine contributed to the poor decision-making.
The report states the supervisor had not been drug tested for 10 years and only 10 per cent of rail workers were tested each year.
The supervisor said he had taken methamphetamine three days prior after the death of a close friend.
"It was unlikely that the rail protection officer was impaired at the time of the incident, although he may have been in the days prior to the incident," the report said.
"The short duration of methamphetamine use would suggest that he was not likely to have experienced chronic impairment by the drug."
This incident is the fourth rail occurrence investigated by the commission where a person at the centre of an investigation has tested positive for illicit substances during a post-incident drug and alcohol test.
The three previous occasions were at North Junction (KiwiRail maintenance worker) in 2011, at Melling (KiwiRail train driver) in 2014 and at Morningside (Transdev Auckland Limited train driver) in 2015.
Kiwirail has confirmed that, from October 1, 20 per cent of its employees will be randomly tested.