"He had been tested a number of times before and all those tests had been cleared," she said.
After the accident the driver was stood down and Ms Hume confirmed he no longer worked for KiwiRail.
In the past 12 months KiwiRail had carried out 950 drug and alcohol tests on 791 people. Of those 1.5 per cent came back positive, she said.
"At any time anyone can be tested for drugs," she said.
KiwiRail is also investigating the incident.
Ms Hume said they would gather information from the black box, and cameras on board, which would indicate how the driver responded at the time of the crash.
Two of the 12 people on board the Matangi train suffered minor injuries and there was substantial damage to the train and stop block.
Overhead electricity wires were also bought down when a power pole behind the stop block was broken.
TAIC deputy chief commissioner Helen Cull said the driver, who had 11-1/2 year' experience driving trains, was tested for drugs and alcohol after the accident.
"His urine sample returned a reading for the active ingredient in cannabis which experts have told us is consistent with a non-chronic user smoking a cannabis cigarette two or three days earlier," Ms Cull said.
"The issue of whether the driver's performance was impaired by cannabis is a further line of enquiry."
Ms Cull said definitive findings as to why the accident occurred had yet to be made.
Data from the train event recorder showed the braking system responded correctly but due to the damage to the train, tests of the complete braking system had yet to be conducted.
Other lines of inquiry were looking at the ability of the trains to stop on a wet or greasy track.
The report also identified a series of urgent recommendations which have been made to operator KiwiRail.
These concerned restricting station approach speeds, upgrading the stop block design to better absorb collision and shifting any poles carrying overhead wires from behind the end of rail lines.
The Rail and Maritime Transport Union (RMTU) said there was a long-standing concern about the effectiveness of the Matangi braking system among train drivers.
The union would work with KiwiRail on interim recommendations in the Transport Accident Investigation Commission report.
RMTU General Secretary Wayne Butson said there had been numerous reports about braking system irregularities
"The sole purpose of the interim report provided was to make urgent recommendations to Kiwirail regarding safety issues identified early in TAIC's ongoing investigation," he said.
Mr Butson said the issue of whether the driver was impaired in any way remains one line of enquiry.
"At this point no allegation of driver impairment has been made, and the RMTU have seen no evidence of driver impairment."
