"The engineers need to understand what they are working with underground before they start building the new intersection," he said.

"These investigations will ensure there are no surprises when construction gets underway in earnest."

Mr Perrett said the $300 million upgrade was fully-funded by the Federal Government.

"The Liberal National Party candidate must now come clean about his plan for this intersection," Mr Perrett said.

"Last I heard the LNP was dead against this upgrade so southside motorists deserve to know where he stands."

Mr Perrett said a design/construct tender would be called later this year.

The new intersection will take Kessels Road under Mains Road improving traffic flow on both roads in both directions.

The upgrade will also include new turn and access lanes, and new provisions for pedestrians, cyclists and buses.

To prioritise safety and to minimise disruption to traffic, most of the early investigative works will be undertaken between the hours of 8pm and 5am.

Mr Perrett said the early works would be completed in approximately two months.