Tim Ellis, SC, clashed several times with Crown prosecutor John Pickering, SC, on day four of the hearing, and was warned by magistrate Chris Webster that he was the defendant, not the prosecutor.

Mr Ellis, Tasmania's Director of Public Prosecutions, has pleaded not guilty to causing the death of 27-year-old Launceston woman Natalia Pearn after a three-vehicle crash on the Midland Highway a year ago.

Mr Pickering wrapped up the prosecution's case against Mr Ellis in the Hobart Magistrates Court yesterday, and defence lawyer Michael O'Farrell, SC, unsuccessfully attempted to get the case thrown out, saying Mr Ellis had "no case to answer".

For Mr Ellis to be guilty of causing the death of Miss Pearn, his driving must have been "conscious and voluntary", and won't succeed if the defence proves Mr Ellis was unconscious at the time of the collision.

Mr O'Farrell said Mr Ellis's driving was a breach of traffic laws but "does not speak of negligence" and the prosecution would not be able to prove the driving was voluntary.

But Mr Webster said he was satisfied there was a case for Mr Ellis to answer, and he was called to the witness stand. Mr Ellis told the court of his long history of sleeping problems, and said he recalled falling asleep on a drive back from Launceston over a decade ago with his children in the car and described it as a "dangerous and frightening" experience.

Mr Pickering asked Mr Ellis if he was worried about the possibility of becoming tired on the day of the accident and Mr Ellis said "no, not really".

Mr Ellis said he would not have pulled over "merely because he was tired".

"That's not where I draw the line," he said.

"Tired is our lot in life".

In a police interview two days after the accident Mr Ellis said he had no recollection of being in the wrong lane or the fatal collision, but yesterday said he remembered "darkness and a whistling noise like a missile landing in a TV show".

"I remember enormous noise, and it's all in darkness," Mr Ellis said.

"On reflection, what I heard is the fatal impact," he said.

"I find it terrifying to imagine I was in the wrong lane".

Mr Pickering said Mr Ellis knew the dangers of falling asleep behind the wheel and had made submissions to a Tasmanian Law Reform Institute paper on the topic.

He asked Mr Ellis if he was just confused about the road markings.

Mr Ellis said it was possible, but it was more likely "that the need to sleep was overpowering".

Mr Ellis told the court he wrote to Miss Pearn's parents after the accident to tell them "there wouldn't be an argument about  her driving" and that he accepted he was in the wrong lane.

Crash investigator Senior Constable Kelly Cordwell told the court on Monday that steering input was required for Mr Ellis to stay in the wrong lane on Spring Hill for up to a kilometre, but Mr Ellis denied much steering was needed to navigate the bend.

In closing his cross examination Mr Pickering said: "I put it to you that it's the case that you weren't asleep when you were on the wrong side of the road."

Mr Ellis replied: "It's possibly the case but I don't think it is the case."

The defence is expected to call one witness today, before closing statements from both sides.