While motorists are right to be frustrated by redundant roadwork signs reducing speed limits unnecessarily, the former general manager of SA's transport department says whacking contractors with a $20,000 fine is a step too far.

It follows a bill introduced to Parliament this week by Member for Narungga Fraser Ellis, who wants to increase penalties from $1,250 to $20,000 if roadworkers leave signs out after a project is completed.

Luigi Rossi, the former department general manager now director of Luigi Rossi & Associates, said some contractors needed to "lift their game".

"There's no question there are situations where the sign that's been left there is no longer required and there is no reason for it to be there," he told ABC Radio Adelaide.

"I just wonder if jumping from $1,200 to $20,000 is necessarily the right amount, but it will definitely draw attention."

Mr Rossi said smaller contractors would not be able to afford a $20,000 fine, although he admitted the current $1,250 penalty was probably not enough for companies to "take notice".

He said one way to overcome the problem could be smarter signs or devices that changed or went blank once workers had left the site and speed reductions were no longer required.

Mr Rossi added, however, there were many occasions when speed limits remained reduced due to motorist safety concerns, even if visible obstacles were not readily apparent to commuters.

He recommended engaging with the construction industry and the Civil Contractors Federation to change practices and create a shift in approach.

Bitumen must cure

When Mr Ellis raised the topic in Parliament last month due to ongoing speed limit reductions south of Port Wakefield, he was told newly laid bitumen took time to cure.

Transport Minister Corey Wingard said it had to have "a certain number of kilometres run over it" and needed to be "retested and re-calibrated before the speed limit goes back up".

"Likewise, line markings, audio tactile line markings, are other things that need to be considered as well," Mr Wingard told Parliament.

"If there are entry and exit points of vehicles that are coming on and off that road as well around a site such as this, where extensive roadworks are happening, sometimes then the speed limits are reduced to make sure it is a safe environment."

But Mr Ellis said the speed restriction — 80 kilometres per hour in an otherwise 110kph zone — had gone on too long.

"It's been months and months of those signs being out and it's time they get lifted."

Mr Wingard introduced $1,250 penalties for contractors in April, largely in response to ongoing hold-ups surrounding South-Eastern Freeway works and motorists being forced to drive slower than necessary.

Motorists vent

ABC Radio Adelaide listeners from across the state complained about similar scenarios, such as outside Mount Compass where the speed limit for a stretch of newly laid road remained reduced for weeks.

"Driving from Keith to Kingston turn-off on Saturday, roadworks signs out … 40-60kph the whole way, no workers. Frustrated drivers driving 80kph+." — Anonymous

"They left restrictions in place for months on the Sturt Highway only because the wire rope hadn't been put back up after roadworks were completed. What's the difference between this and a highway that doesn't have the rope barriers?" — Larry

"Two weeks ago between Meningie and Tailem Bend there were two speed restrictions, no-one there, no witches hats, no sign of a recent accident or tree fallen or roadworks, absolutely no reason." — Leigh

"Speed limited on Old Mt Barker Rd yesterday. NOOOO sign of roadworks anywhere. Sooooo annoying. No more outsourced road signs. At the end of the so-called roadworks, they put the wrong speed up. 60 not 50! The roadworkers themselves must put the signs aside for the sign contractors to pick up." — Caroline

Mitigating risk

One contractor told ABC Radio Adelaide that it was "hard enough trying to keep people employed" without being "threatened by government with more punitive measures".

"Motorists drive through a speed-reduced work zone thinking nothing [is happening]," the contractor wrote in a text.

"It is our responsibility to keep everybody safe.

"I'm mitigating risk and I'm reducing speed, and if that inconveniences motorists, well then that's what has to happen."

But Mr Ellis said he was not arguing to lift speed limits while workers were there nor while roadworks were underway.

"By all means, continue to have those restrictions in place, but when they're done or finished, there should be some consideration given to the motorists," he said.

Mr Ellis said he had received some anecdotal support from other MPs since introducing his bill, but with just four sitting weeks left in the year, and a "congested list of private members bills", he will have to "push hard" to get his bill considered.