Todd Andrew Killiner, 54, was behind the wheel of a road train when it left the road, went down an embankment then flipped over about 87km from Newman in October 2017.

Corey Bluntish, 37, was asleep in a resting place behind the driver's seat and was trapped in the cabin when it was engulfed by fire, while Killiner escaped with minor injuries.

The District Court of WA heard the pair would alternate shifts lasting a maximum of five hours and Killiner was nearing the end of one of those stints when the crash occurred.

Prosecutor Sean Dworcan told the jury Killiner tended to work while tired and a driver monitoring system that detects fatigue captured him my closing his eyes for longer than 1.5 seconds on 25 occasions between April and September that year, triggering a loud alert and seat vibrations.

Fed up with them, he turned the camera so it could not capture his face, Mr Dworcan said.

Tyre impressions in gravel on the side of the sealed, straight, flat and dry highway showed the truck had gradually departed from it, "consistent with a driver who had fallen asleep".

The prosecutor said Killiner lied when he claimed he heard a bang or pop before the prime mover veered to the left, which he could not steer out of, suggesting a front tyre had blown.

There was no evidence to support that claim, such as gouge marks in the road.

In an interview before he was charged, Killiner told detectives he didn't wear his seat belt because "I want, if something goes wrong, to get out".

He said he might not have been able to flee the crash if he had been wearing it.

Asked if he had felt sleepy, Killiner replied "not that I know of".

He faces a sentencing hearing on October 15.

Australian Associated Press