Prime Minister Tony Abbott said this week he hoped the Commonwealth's $400 million commitment over 10 years would be enough to make it a four-lane highway between Launceston and Hobart.

"It'll certainly make a pretty big difference," Mr Abbott said. "I hope it will."

Similar major road works have been funded 80 per cent by the federal government and 20 per cent by the state, but the new state government is yet to commit to its share.

Mr Abbott said that was not the subject of his discussions with the state government during his visit to Hobart.

"I'm not talking to them about it at this instant," Mr Abbott said.

"In the end, this is the kind of thing that we will be working in partnership with the Tasmanian government to achieve."

The federal money is set to flow from July 1 with $40 million allocated in 2014-15, but there are still no details about where and when work will start.

A Department of Infrastructure, Energy and Resources spokeswoman said yesterday planning and project scoping was under way for several areas along the Midland Highway.

She named the Perth to Breadalbane section and a south- western bypass of Perth as key priorities.

"Geometric configuration, junction options and preliminary investigatory works for upgrading the safety and efficiency of the Perth-Breadalbane section of the Midland Highway" and "route and junction options for a south- western bypass of Perth, linking the Midland Highway to Illawarra Road" are being worked on.

She said the department was also reviewing the latest AusRAP report on road safety to identify safety improvements along the Midland Highway to achieve a consistent high-safety rating for the whole road.

The Coalition government's contribution was confirmed in last week's federal budget.

It is $100 million less than what was promised by the previous Labor government, which has criticised the Coalition government's contribution as far short of what is required to duplicate the road.