Roadworks that create significant traffic congestion in Adelaide will soon attract hefty fines for the contractors involved if the hold-ups are considered unnecessary.

Adelaide traffic growth There are 1,764,396 registered vehicles in SA

There are 1,764,396 registered vehicles in SA This is about 43,000 more vehicles than people

This is about 43,000 more vehicles than people Vehicle registrations are up 35 per cent since 2000 (Department of Planning, Transport and Infrastructure)

From next June, South Australian roads will be grouped into three categories based on traffic volumes or levels of heavy vehicle use, with contractors required to pay for permits for work during designated times of the day.

The new system will encourage work to be done outside of the busiest times on the arterial network and reduce the roadworks delays, Transport Minister Stephen Mullighan said.

"Tough penalties will help to deter organisations which are careless or blatantly ignore the impacts that restricting the flow of traffic can have," he said.

He said fines of $1,250 would apply to agencies or contractors which blocked off traffic lanes or reduced speed limits without a permit, or failed to comply with their permit conditions.

New legislation allows for a maximum court-imposed penalty of $20,000 for a first offence and up to $50,000 for further offending.

Permit charges for works will vary from $500 per hour for major roads to $250 per hour for other main roads and $100 per hour for minor roadways.

Signs must be removed at other times

Mr Mullighan said speed restrictions would have to be removed when there were no workers present and the road conditions were not a danger.

Roadworks projects will need to be more mindful of traffic impact under the changes. ( Supplied: SA Government )

Adelaide motorists should be able to expect a quicker commute, motoring organisation the RAA said.

Senior road safety manager Charles Mountain told ABC Radio Adelaide the new permit and fines system should go a long way toward improving city and suburban road flows.

"One of the issues that we receive the most complaints about is the roadworks taking place on major arterial roads and particularly the roadworks being kept in place, along with speed restrictions, when it doesn't appear that there's any actual work taking place," he said.

"Of course work has to take place to maintain the road network and make improvements where necessary, but a better level of control hopefully will reduce the level of congestion and frustration motorists currently experience."

Higher costs for councils

Local Government Association president Lorraine Rosenberg said councils would face higher costs for works they undertook, often at short notice, such as filling dangerous potholes.

"Most of the works that come up quickly or urgently are those that somebody will ring in to us as a local government authority," she said.

"In terms of the cost to us of permits, I guess we would say that is just another way of government making money.

"It definitely will add costs to roadworks."

Ms Rosenberg said it was pleasing the legislation provided for urgent works to be done within a two-hour window, provided the transport department was notified.

She said local government would ensure it helped both motorists and its own workers who maintained public roadways.

"We will make this work because we have to make it work," she said.

The SA Government said the new permit system would help the Traffic Management Centre coordinate roadworks and give advanced warning via the AddInsight app and Traffic SA website.