The partner of a B-double log truck driver involved in a fatal accident has given evidence in a Warrnambool trial

Peter Buckley, 61, of Mount Gambier, is appearing in the Warrnambool County Court charged with 10 offences - culpable driving causing death, dangerous driving causing death and four counts of negligently causing serious injury and the four alternate charges of dangerous driving causing serious injury.

The charges relate to a fatal collision on the Portland-Nelson Road near the intersection of Westlakes Road about 2.30pm on March 14, 2018.

A court heard Mr Buckley was driving a fully-loaded log truck south on the Portland-Nelson Road when it collided into three stationary vehicles at roadworks, killing a 57-year-old woman from the United Kingdom and seriously injuring four other people.

His former partner Amanda Haggett said she feared that Mr Buckley would kill someone if he suffered what he described as a déjà vu episode when he was behind the wheel of his B-double log truck.

Early on in their relationship she recalled seeing Mr Buckley clasping his fists while watching TV and he called her by his previous partner's name.

Ms Haggett told the court Mr Buckley explained he had suffered a head injury as a younger man in the United Kingdom and he had to take medication morning and night so he could drive.

The visibly upset witness said she and Mr Buckley went to the Riverland and on the way home to Pinnaroo Mr Buckley veered off the road.

"I screamed. I didn't know what was going on. He had run off the road. He eventually stopped the car. He said he had just fallen asleep," she said.

"Before the incident he was clasping his fists. The next day we talked. We had a massive argument over it. He was going to move back to Mount Gambier. He had started packing his bags.

"He calmed down and it was fine. I just wanted to know what was going on. I just needed to know."

Ms Haggett said Mr Buckley told her when he got tired he suffered episodes.

"We argued. He wouldn't take his medication. I didn't want him to drive," she said.

"I was scared he was going to hurt someone. I was scared of him having a turn while he was driving. They would come all of a sudden."

The woman said she started monitoring Mr Buckley's medication, which instructed on the packet to take it each morning and night.

"He wasn't doing it," Ms Haggett said.

"Peter took them when Peter wanted to take them. Peter didn't want to take them and he didn't," she said.

When Mr Buckley suffered an episode, Ms Haggett said he would clasp a fist or both fists and his tongue would move like he had a dry mouth.

"He wasn't there. He was home, but he wasn't home. He would go pale, I don't know how to describe it," she said, adding the episodes started once every four of five weeks and towards the end of their relationship they were every day or second day.

"It was so often in the end it was just part of our life. There was no real trigger, there was no pattern."

The witness said Mr Buckley lost a truck driving job at the end of 2016 after bogging a truck off the road and he got his old job back at Mount Gambier in the log truck.

She said Mr Buckley laughed about bogging the truck off-road and the couple continued arguing but were living separately while their relationship continued.

The witness said the arguments were about the same thing - Mr Buckley not taking his medication.

She said in the end Mr Buckley was having turns every day and they were having daily arguments.

Ms Haggett said in February 2018 Mr Buckley had his annual medication appointment with his neurologist and she went with him but waited outside.

"He definitely told me he was telling the doctor about his deja vu events," she said.

"I ask him if he told the doctor about turns and he said he did. I was so excited he got to keep his licence.

"Peter assured me he told the doctor about his deja vu events and I believed him."

Ms Haggett said Mr Buckley was concerned about the episodes because he was scared about losing his job and he needed the money.

She said the weekend before the fatal collision she noticed Mr Buckley was not himself.

"He had a turn on the Saturday. He was not himself. He always came out of them," she said.

"In the end when we would have a turn we would not discuss it because we would argue.

"Sunday was a really bad day. He was not himself. We argued. He had a turn. I pretended I didn't notice and I walked away.

"A few hours later he had a turn. He went and played golf and he had another turn.

"I said to him he was going to kill someone.

"We didn't speak the next day. I didn't want the relationship any more. He had another turn on the phone, he was not coherent and I hung up.

"We discuss medication all the time, whether he was taking it. I was so worried."

Ms Haggett said on the day of the collision Mr Buckley wasn't well.

"He told me he had a headache, he was tired and he looked pale. I knew he wasn't right. I told him to please pull over and have a rest or just go home.

"I just wanted him to go home. He told me he would be all right. He told me he had to get logs to the place."

Ms Haggett said that afternoon she got a telephone call that Mr Buckley had been involved in a fatal accident.

She said Mr Buckley told her couldn't remember the accident and the next day he went to see a doctor.

"The doctor asked if he had any medical episodes in the past and Peter said 'no'," she said.

"I walked out of the doctor's office. I couldn't stay there. I felt sick because he was lying and I wanted to tell the truth."

Ms Haggett said she spoke to Mr Buckley a couple of times but that was the end of their relationship.

On Monday the trial before Judge Quin heard from a number of expert medical witnesses, including neurologist and epileptologist Professor Mark Cook.

Professor Cook told the court that he believed Mr Buckley suffered a "complex seizure" at the time of the accident.

He said possible sleep deprivation and missed medication could have led to a seizure.

Professor Cook agreed Mr Buckley was prescribed Sodium Valproate and while the level of medication found in his blood after the incident was low, he believed it was still an "effective" level.

The trial will continue on Tuesday.

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