A solo father of three who drowned after his car went into a river on the West Coast may have been impaired by his cannabis use, a coroner has found.
Tamati James Rae died in September last year, after hitting a one-way bridge and plunging into the river on Atarua Road in the Buller District.
Mr Rae, 32, was trapped in the vehicle, and drowned as a result.
His three children were rescued from the upturned and submerged vehicle by a passer-by.
Mr Rae had left his children with family in Hokitika while he was away for the weekend. The accident happened as he was driving home to Kaikōura on the Sunday evening.
The report said Mr Rae's parents had tried to encourage him to remain with the children in Hokitika for the night, but Mr Rae indicated he needed to get home for work.
Just after 8pm on 10 September last year, Mr Rae drove into the end of the Rough River Bridge, causing the vehicle to overturn and land in the river below.
Andrew Field, who rescued the children, drove on to the bridge soon after. He noticed parts of the guard rail were missing and debris from the crash before he looked over the side of the bridge and saw Mr Rae's vehicle upside down in the river.
When he reached the vehicle he realised there were children in the back seat. He smashed a rear passenger window with a rock, and removed the children to safety before returning to try and rescue Mr Rae, but was unable to open the door to get him out.
Mr Field was commended for his bravery and quick actions, which prevented a possibly much greater tragedy, the coroner said.
The police report showed that neither the weather, road conditions nor excess speed were factors in the crash, but the initial impact area showed that Mr Rae did not correctly align the vehicle with the entry on to the bridge.
The impact caused the vehicle to spin before it crashed through a wooden barrier and teetered on the edge before it pitched forward and landed on its roof in the river 4.2 metres below.
Toxicology tests showed Mr Rae had recently used cannabis.
The coroner's report said it was possible that as a result, Mr Rae failed to recognise the narrowing road leading onto the one-way bridge, and crashed.
The Crash Investigation Report said that an extension of metal barriers across the bridge may have made the crash survivable.
The bridge was on the territorial boundary between the Buller and the Grey District Council, and was managed by the Grey District Council.
The council said it agreed with the coroner's findings, but installation of the specific Armco barriers was complicated by the narrow width of the bridge which was regularly used by large trucks and farm vehicles.
The transport agency is currently seeking additional national funding to enable a programme of replacement of timber bridge rails with Armco barriers throughout New Zealand.
The coroner said the circumstances in this case justified such replacements.