Adam Robertson, 35, hadn't slept for days when he veered onto the wrong side of the Bass Highway on February 26 last year, killing Shane Williamson and Rodney Rowe who were on their way to work.

All three men died at the scene, while the two children remarkably escaped serious injury.

In findings published on Thursday, coroner Andrew McKee said he couldnt make a precise ruling about what caused Mr Robertson to cross into incoming traffic.

"I am, however, satisfied that the ingestion of methamphetamine by Mr Robertson played a significant part in this collision occurring," he wrote.

"The consumption of that drug caused him not to sleep in the days preceding the collision."

Mr Robertson violently assaulted his partner in the hours before the crash, leaving her hiding in a shed, put their children in the family car and drove away.

Two men who witnessed the crash immediately called triple zero and, along with other members of the public, assisted as best they could until emergency services arrived.

Methamphetamine was found in Mr Robertson's blood during an autopsy at 8.5 milligrams per litre, an amount described by an expert as a "high concentration".

Mr McKee ruled the collision was entirely Mr Robertson's fault and noted neither car had defects and speed was not a factor.

Mr Williamson, 65 and a father of five, took evasive action in an attempt to avoid the crash.

"This case is another example of the consequences that flow from individuals driving motor vehicles after consuming illicit substances," Mr McKee wrote.

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Australian Associated Press