All train drivers should face compulsory drug testing after an inquiry into the Melling station crash revealed the driver had used cannabis, a detection agency says.
The driver has since been sacked - and employer KiwiRail said 14 staff had returned positive drug tests in the past year.
Over that time, KiwiRail has done 950 drug and alcohol tests on 791 of its 4500 staff.
Despite this, KiwiRail insists there is no drug problem within the company.
Passenger general manager Deborah Hume said the driver, who had more than 11 years' experience, no longer worked for the state-owned rail operator. She declined to comment on the reason why.
The Transport Accident Investigation Commission yesterday released interim findings into the crash on May 27 that saw a Tranz Metro passenger train overshoot the end of the line, bringing down power lines and injuring two of the 12 people on board.
It was the second such incident at Melling, Lower Hutt, in just over a year, prompting the commission to issue a raft of urgent safety recommendations yesterday.
Deputy chief commissioner Helen Cull, QC, said the driver was found to have THC acid - the main psychoactive substance in cannabis - in his urine at a level of 60 nanograms per millilitre.
The level was consistent with a non-chronic user smoking a cigarette two or three days earlier, she said. It was not clear exactly when the drug was taken.
The commission was investigating whether the driver's performance was impaired by cannabis at the time and whether he had been operating trains two or three days earlier.
It was also looking at the performance of the train's brakes, slippery conditions and the adequacy of driver training at KiwiRail as possible factors in the crash.
Cull said the commission had voiced its concern several times in the past about transport operators using drugs, and she would be worried if the trend continued.
Hume said the driver had been randomly drug tested three times since 2006 and returned clean results every time.
Of the 14 people who had returned positive tests, three were from the 500 staff who work in KiwiRail's passenger division, which includes its 100 drivers.
The data showed there was no drug problem within the company, as the number of staff getting caught was well below the national average of 6 to 7 per cent, Hume said.
New Zealand Drug Detection Agency spokesman Kirk Hardy would not comment specifically on the train crash but said cannabis was particularly problematic for driving because it could impair motor skills for days, long after the ''high'' had worn off.
''There is a misconception that just because you're not high any more there is no risk,'' he said. ''That's wrong.''
Based on drug-testing figures, cannabis use in the transport industry was lower than other industries but the stakes were far higher.
''Every industry faces these problems but in transport when things go wrong they go wrong on a big scale and it can have disastrous consequences.''
Many transport businesses already drug-tested drivers but it was far from universal, with cost often cited as a factor. Many countries overseas already had compulsory drug testing for the transport industry and New Zealand needed to catch up.
'''Self-regulation just doesn't work.''
But even with the most rigorous drug testing, it was difficult to stop people working impaired, even in high-risk industries, he said. ''There are always going to be people who want to run the gauntlet.''
Rail and Maritime Transport Union general secretary Wayne Butson said impaired drivers were very rare but should not be tolerated.
''You never know when someone might walk out in front of your train.''
Crash investigators are unsure whether brakes were to blame for the Melling train crash in May.
An interim report of the Transport Accident Investigation Commission's inquiry describes how the train driver rounded the final bend to the station and, realising the train was not going to stop in time, alerted passengers to brace themselves.
The train's wheels slid several times on the apparently wet track as the brakes were applied.
The train event recorder showed the brakes had the correct air pressure and responded correctly to the driver's inputs.
But, because the brakes were badly damaged, the commission had been unable to fully test them and could not rule out malfunction at this stage.
Deputy chief commissioner Helen Cull, QC, said the crash happened just as the Sun's rays were hitting the track and humidity in the area had reached its peak.
The commission was looking at whether humidity could have made the track slippery and how effectively Matangi trains can stop on a wet or greasy track.
The crash in May follows a similar incident at the same station in April 2013, when another train smashed through the end-of-line blockade.
The commission hopes to finish its full investigation into both incidents by March next year.
WHAT THE INVESTIGATOR RECOMMENDED
A permanent speed limit on the last section of the Melling Line.
All other terminating stations throughout the country be assessed and have speed limits applied as necessary.
The concrete stop block at Melling be replaced with a new shock-absorbing design.
The overhead electricity line at Melling Station be moved from behind the stop block.
WHAT KIWIRAIL HAS DONE ABOUT IT
Applied a 25kmh limit to the approach at Melling and Johnsonville stations.
Reduced the speed limit for the entire Melling line from 70kmh to 50kmh.
Extended the stopping distance for trains approaching Melling Station.
Assessed the approach speeds and stopping distances on all rail lines in the Wellington metro network that have stop blocks.
Begun designing a shock-absorbing stop block for Melling Station.
- The Dominion Post