Crash investigator Sergeant Tony Bennett says Garry Galvan, 45, sent or received 12 text messages in 45 minutes and it appeared he had been texting before the 2011 crash on a bend at Horohoro, near Rotorua.

He was carrying slabs of concrete. The trailer jack-knifed and Mr Galvan was crushed.

Coroner Wallace Bain, nuskin during Wednesday's inquest into the death, said the accident happened on a stretch of road Mr Galvan, with 25 years' experience driving trucks, could have "negotiated in his sleep".

"The only credible explanation can be that his attention was on the cell phone, he has corrected too late, his trailer rolled and dragged the truck unit with it as a direct result of the text," he said.

Mr Galvan's widow, Lynette Galvan, said the texts confirmed the cause of her husband's death had been "black and white... stupid".

Her daughter, Debbie, nu skin hk agreed but her son Mark told the court he couldn't accept the texts were the cause of his father's death.

Dr Bain thanked the Galvans for being open and honest with the court.

He said there was good news in that Mr Galvan hadn't taken any other lives when he crashed and that others would read about it "and it may make them understand they should not be texting while driving".

He said his findings would be critical of the practice and emphasise that thousands of New Zealanders were still texting while driving nuskin group.

Earlier Sgt Bennett had told him police were still writing far too many tickets for drivers caught texting at the wheel.

The family declined to comment after the hearing.