A man accused of the manslaughter of a man he punched into the path of a rubbish truck on a busy Brisbane motorway was acting in self-defence, his trial has heard.

New Zealand man Tamate Heke was driving home from a 12-hour shift when he was tailgated and challenged to pull over on the afternoon of December 1, 2015, the Brisbane Supreme Court was told on Monday.

During the trial's opening, the jury was shown CCTV of the alleged attack in which Heke and Shane Merrigan argue after stopping their cars near an exit on the Gateway Motorway.

Tamate Heke told police he tried to catch Shane Merrigan as he fell over after being hit. Photo / AAP
Tamate Heke told police he tried to catch Shane Merrigan as he fell over after being hit. Photo / AAP

Heke's defence barrister Joshua Fenton said his client had been pushed twice and punched in the face before striking Merrigan.

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That blow caused Merrigan to topple backwards onto the motorway where he was run over by the rear wheels of a rubbish truck.

Heke later told police he tried to catch Merrigan as he fell over after being hit.

When asked why he punched Merrigan, Heke told investigators he wanted him to "back off", Fenton said.

Crown prosecutor David Meredith, however, argued Heke had never been pushed or hit by Merrigan.

"Shane Merrigan did not even touch him," he said.

"Shane Merrigan approaches (Heke) but makes no further move towards him and while he might be speaking he does not strike or even threaten to strike the accused by his physical movements."

Heke is seen sitting on the side of the motorway with police at the scene. Photo / Channel 9
Heke is seen sitting on the side of the motorway with police at the scene. Photo / Channel 9

Both sides agreed the CCTV evidence would be critical to the cases they were putting to the jury.

Several eyewitnesses are due to give evidence during an expected two-week trial before Justice Peter Applegarth.