Drugs played a "direct role" in the crash which killed Chris Tobin and his 16-month-old son Jack Kronfeld-Tobin, after Tobin drove across a flush median and into the path of an oncoming double-decker bus, the Coroner has found.
Tobin died of chest injuries at the scene and Jack of a cervical spinal cord injury, succumbing in his mother's arms at Starship Hospital three days after the July 2017 crash in Auckland's Mt Eden.
Tobin's older child, 2-year-old Elle, survived skull fractures suffered in the crash, while two of the half a dozen bus passengers received moderate injuries.
In recently released findings Coroner Katharine Grieg wrote that the police investigation noted evidence Tobin appeared to have been driving in a normal manner immediately before the crash.
But the 51-year-old was then seen to drive straight through a bend and onto the other side of the road without accelerating, slowing down or braking.
"The investigating officer concluded that distraction, from the unrestrained dog in the car or another factor, was a possible contributor to the crash."
Post-mortem toxicology results also identified methamphetamine and amphetamine in Tobin's blood, along with GHB, a powerful central nervous depressant, Grieg wrote.
"While it could not be known whether he stopped concentrating, was falling asleep or was otherwise impaired, taking into account all the evidence, the Coroner was satisfied that drugs played a direct role in the crash."
It wasn't necessary for her to make any recommendations relating to Tobin's drug driving as its dangers were increasingly being recognised, including through a 2019 New Zealand Transport Agency social media and TV campaign to raise awareness.
A copy of her findings would be sent to the agency's chief executive, along with the New Zealand Drug Foundation, to highlight the circumstances of Tobin and his son's deaths.
Her findings would also be sent to the chief executives of the Ministry of Transport, Plunket, Safekids Aotearoa and Auckland Transport to highlight the circumstances of Jack's death, after it was found aspects of the use of Jack's child restraint could have been improved, and increased the boy's safety in the crash.
Jack was in a forward facing Safe-n-Sound Meridian AHR child restraint, an approved restraint under New Zealand standards, and it was secured by a seat belt.
But tether (anchorage) straps were not attached to the car and it was suggested a rear-facing restraint would have been safer, "per Plunket's advice that babies be kept in a rear-facing restraint until at least two years of age", Grieg wrote.
"The issue of a mandatory requirement for rear-facing child restraints for children under two years, and compulsory use of tether straps, are not matters that it is appropriate for me to make recommendations on in this case.
"However, the issues related to child restraints raised in the course of this inquiry are concerning and important in relation to saving children's lives and it appears that there is varying and conflicting information available to New Zealand parents on these issues."
Clear information for parents and caregivers and consideration of strengthening of the regulatory framework might prevent deaths in situations similar to the crash which led to Jack's death, she wrote.