A few kilometres before a vanload of Australian school students smashed into a milk tanker killing the driver and a teenage passenger, it was seen to swerve over the centreline, then correct.
The witness, who was travelling behind the minivan, saw it again drift over the centre line into the path of the on-coming tanker.
This has raised the possibility the driver may have been fatigued or drowsy, something that led to the adjournment of the inquest into the resulting two deaths.
Bay of Plenty district Coroner Dr Wallace Bain made the decision after hearing evidence into the deaths of teacher Andre Daniel Vogel, 36, and Gabriel Conor Runge, 16, in the Rotorua Coroners Court today.
Mr Vogel had been leading a group of Noosa Pengari Steiner School students on a tramp across the Tongariro Crossing before the minivan crash at Reporoa at 4:30pm on November 28 last year.
Another student was left critically injured.
Dr Bain adjourned proceedings to give expert witness Major Charmaine Tate of the New Zealand Defence Force the chance to read the transcript of earlier evidence and reports prepared on behalf of the school.
Major Tate is an Army expert in survival medicine.
The coroner said it was important the court looked very carefully at fatalities involving drowsiness, how they occur and can be prevented in the future.
Gabriel's parents posed a number of questions to witnesses, Major Tate included, about the likelihood of Mr Vogel being over-tried when he drove the students on the two-hour trip from the mountain to Rotorua.
He was the school's outdoor education teacher and Gabriel was a pupil at the school.
The school was linked to the court by a trans-Tasman phone link and a teacher who had been in the van when the fatalities occurred gave evidence via it.
She said she had been asleep when the crash occurred.
Evidence was given that all but one of the students had been asleep too. The one who had remained awake told police that immediately before the crash she saw Mr Vogel's hands slip off the steering wheel and head slump to the right.