The Transport Workers’ Union says operators who allow unsafe vehicles on to the road should face jail.

South Australia branch secretary of the TWU, Ray Wyatt, says jail time should be on the table rather than financial penalties.

Mr Wyatt says he was shocked after a police operation last month should that nearly half of all heavy vehicles pulled over in Adelaide were driving with a significant mechanical defect.

While the companies involved will be fined, and lose some money from the downtime taken for repairs, Wyatt says normal penalties are not enough to change the industry.

“It's when people are actually penalised and incarcerated for causing deaths on our roads [that] we'll have safe roads in Australia,” Mr Wyatt told industry media.

“Until directors and CEOs go to jail, there will continue to be this squeeze where it's all about the bottom line and dollars for shareholders.”

Mr Wyatt was speaking in response to the findings of Operation Shake Up, a sweep of heavy vehicles’ road worthy compliance in late April.

Of 63 heavy vehicles inspected, 31 were found to be defective, with ‘major’ defects such as brake and steering issues on any of them.

Several vehicles could not even be driven away, and had to be towed to a place of repair.