An alleged drunk driver who fatally struck a drug-affected motorcyclist in Perth has been cleared of being criminally responsible.

Patricia Connie Peters stood trial in the West Australian District Court accused of dangerous drunk driving causing the death of 23-year-old Damir Nezic at a Morley intersection in June 2017, but was found not guilty this week.

Ms Peters, then aged 37, had an alcohol reading of 0.186 per cent while Mr Nezic had methylamphetamine in his system, the court heard.

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Mr Nezic’s helmet came off during the collision and he died at Royal Perth Hospital from multiple injuries.

One witness became emotional while testifying about the “traumatic” incident, saying he saw Mr Nezic overtake him and at the same time Ms Peters began moving her car at the intersection.

Witness David Ireland, who was driving along Crimea Street at the time of the incident, told the court he noticed Mr Nezic travelling about 60 metres behind him for about 1km before he started to get closer.

He said he heard the motorbike’s engine “rev up” and then saw Mr Nezic in his right wing mirror begin to overtake him.

It was at the same time, he said, he noticed a Holden Commodore stationary on West Lake Road trying to cross the busy dual carriage way.

He explained when he noticed to Holden Commodore trying to cross he took his foot off his accelerator but at the same time he saw the motorbike speed up and go past him.

“It was almost instantaneous, almost exactly the same time,” he said.

What followed next, Mr Ireland said, was traumatic.

Ms Peters will face Perth Magistrates Court next week charged with driving a motor vehicle under the influence of alcohol.