A sleep researcher who claims the road works for Adelaide's O-Bahn extension project are keeping him up at night has signalled he is preparing to take legal action against the contractor.

Professor Drew Dawson said roadworks near his home on Hackney Road began a fortnight ago, and he believed contractor McConnell Dowell was exceeding night-time noise limits.

"Our bedside [noise] levels in the house are between 70 and 80 [decibels] and the peak levels are between 90 and 100 when the trucks are clunking and the reversing signals go on," he said.

He said the contractor needed to keep the noise down to 40 decibels at night.

Professor Dawson said when he raised concerns about sleep deprivation the site manager laughed, so he contacted Transport and Infrastructure Minister Stephen Mullighan's office.

"We have tried to be reasonable ... [but] we are planning legal action within the next week," he said.

Transport Department Jon Whelan said the project was exempt from noise restrictions.

He said the louder work was happening during the day, and there were "respite days".

Mr Whelan said the average noise reading for Hackney Road was "around 65 to 70 decibels".

The project will install new bus lanes in the middle of Hackney Road, widen the bridge and create tunnels at the North Terrace end of the project.

The project is expected to be completed at the end of 2017.