That day had started with nervous excitement for Alister Spong, who told the court he had driven his 1942 Ford Jailbar 1500 kilometres down from Queensland for Canberra’s annual car festival.

The festival is the “be all and end all of the modified car scene”, Mr Spong told the jury, and he had a car modification business.

The truck had come from a scrap heap but he had since invested in it $40,000, including a turbo engine, and he had brought it to Canberra as the “showpiece” of his skills.

But when he tried that day to spin the truck's wheels the attempt failed. The truck lurched forward, and his friend Luke Newsome, 30, fell from the tray and later died from a head injury.

Mr Spong, 33, told the ACT Supreme Court that since the death of his friend Mr Newsome following the fall on January 5, 2017, he had not driven the truck. “I can’t,” he said, choking on his words.

He had pleaded guilty to negligent driving. But prosecutors contend Mr Spong’s driving that day met the threshold for the more serious charge of culpable driving, to which he has pleaded not guilty.

The charge alleges Mr Spong failed "unjustifiably and to a gross degree" to observe the standard of care that a reasonable person would have in all the circumstances.

Mr Spong said he was driving about 10 kilometres an hour on the festival's cruise route, a ring road around the festival, when he tried a "chirpie" - or to briefly lose traction - but failed.

He said instead of the “chirping” noise he expected when he released the clutch, the wheels "bit" into the bitumen and the truck suddenly surged forward, causing his friend to fall from the tray.

In her closing address to the jury, prosecutor Margaret Jones said it was natural to feel sympathy for Mr Spong or the fate of Mr Newsome after what had happened.

But she said Mr Spong was responsible for the safety of his passengers and had “experimented” with a manoeuvre in new circumstances, with five people sitting on the tray.

“He tried it for the first time at Summernats and it had tragic results,” Ms Jones said.

She said the incident was a tragedy, but not an accident, and Mr Spong had intended to spin the wheels. The Crown did not have to prove he intended to hurt anyone, she said.

Defence barrister Steven Whybrow said Mr Spong was not a "hoon" and nor was he driving like a "ratbag".

He suggested the jury would have difficulty being satisfied Mr Spong's actions met the threshold for culpable driving, or that there had been  any real risk of injury or death.

He was driving 10 kilometres an hour when he tried a minor wheel spin and it failed, causing Mr Newsome to fall from the 60 centimetre high tray and die, he said.

Mr Spong made an error of judgment and had not accounted for the extra weight of the people on the back, he said.

Mr Whybrow said it was a tragedy, but "we're not here to convict because of the outcome."

The trial continues.