Driver fatigue has been identified as the key factor in the deaths of an Australian school teacher and pupil.
Andre Daniel Vogel, 36, and Gabriel Conor Runge, 16, died instantly when the mini van Vogel was driving smashed head-on into a milk tanker at Reporoa, near Rotorua, on November 28, 2014.
A reserved decision into the cause of the pair's death was released on Tuesday by coroner Dr Wallace Bain.
Dr Bain presided over the inquest last year into their deaths and the crash that injured nine other pupils and a teacher, some seriously.
All came from the Noosa Pengari Steiner School in Doonan, Queensland, and had been in New Zealand on an outdoor education trip to Tongariro National Park, which students described as challenging and exhausting.
Vogel had been one of two teachers escorting them.
The coroner based his findings on evidence heard and a subsequent report from Major Charmaine Tate, a New Zealand Army doctor and expert in the effects of sleep deprivation.
The inquest heard that shortly before the crash a driver had seen the mini van swerve to the left and the driver suddenly take evasive action. The only student awake when the crash occurred saw Vogel's hands slip from the steering wheel and his head loll to the side.
At the inquest in November 2015, Runge's parents raised a number of issues including criticism of the school for having no standard of care for their children and for having no management strategy in place. They also raised the issue of neither teacher monitoring each other's fatigue levels.
The coroner commented that had Mr Vogel appreciated the extent of his fatigue he would not have driven the two-and-a-half hour journey to Rotorua, acknowledging that since the double fatality the school had taken steps to prevent a re-occurrence.
He said organisations and drivers need to take extreme care and vigilance where strenuous activity was involved before a road trip and that drivers are properly monitored.
Dr Bain said it was obvious Mr Vogel was a devoted teacher to his students.
"It seems clear, however, he did not act on the symptoms within himself leading to the drowsiness that occurred."
He concluded the cause of both deaths was traumatic brain injury caused by a motor vehicle accident.