A truck driver who killed a motorist when he went through a red light at one of Perth's major intersections was on parole for drug dealing and had traces of methylamphetamine in his system, the WA Supreme Court has been told.
David Lawrence West has pleaded guilty to unlawfully killing 55-year-old Moira Dunstall in April last year, but disputes that the methylamphetamine, or ice, found in his blood impaired his driving.
West was driving a prime mover and towing a fully loaded semi trailer — weighing 39.4 tonnes — when he failed to slow down as he approached the intersection of Tonkin Highway and Armadale Road, despite being warned by flashing amber lights that the traffic lights were about to change.
State prosecutor Kim Jennings said it was estimated West was travelling at a speed of between 80 and 100 kilometres an hour as he entered the intersection and slammed into Ms Dunstall's car, as she turned right on a green arrow.
She died at the scene.
The court heard about an hour and a half later, a sample of West's blood was taken, and it was found to have a level of methylamphetamine of 0.06 milligrams per litre of blood.
Prosecution argues drugs 'a contributor'
Ms Jennings said West later revealed he had a restless night's sleep the night before after taking Viagra, but he maintained he had felt fine when he arrived at work.
She also said at the time of the crash West was on parole, serving a term that was due to expire 12 days later, for the offence of possessing methylamphetamine with intent to sell or supply.
Ms Jennings said it was the prosecution's case that West's driving was impaired by the drugs in his system, either through fatigue or a lack of concentration.
"It is a contributor to why he ignored or failed to see the flashing amber lights," she told the court.
"There could be other reasons, but the state says it is a contributor."
Sleep disorder may be to blame: defence
West's lawyer, Alana Padmanabham, said it was accepted West should not have been driving with any level of drugs in his system, but claimed fatigue, possibly because of undiagnosed sleep apnoea, could be the explanation for the crash.
"We accept he must have been fatigued, there doesn't seem to be any other explanation [for the crash]," she said.
"The question is, what caused the fatigue? Was it methylamphetamine or undiagnosed sleep apnoea?"
Ms Padmanabham told the court her client admitted using methelyamphetamine on the Saturday night, before the crash occurred on the Monday.
But she said the level of drugs detected in her client's blood was very low, and there was no evidence of any other concerns about his driving on the day.
Toxicologist David Joyce testified that while the level of drugs detected was "relatively low", it pointed to prior use of methylamphetamine and the likelihood West may have been in "the coming down phase" of his drug use.
Professor Joyce said during that phase, people felt fatigued and show a lack of attention.
Members of Ms Dunstall's family attended court for the hearing, which was called to determine the factual basis on which West will be sentenced.
Justice Paul Tottle will sentence him on January 12.
West's bail was renewed until then, but Ms Padmanabham said her client was expecting to receive am immediate term of imprisonment.
