The big ticket item for the ACT is $87.5 million for the Molonglo River bridge, which would require matched funding from the territory government.

Connecting Belconnen to the growing population in the Molonglo Valley, construction on the proposed bridge on John Gorton Drive could be started within 12 months, according to the ACT government.

As recently as August the ACT government said the project couldn't be fast-tracked and was still in detailed design phase.

A further $50 million has been earmarked for a package of upgrades for Canberra's south-west. It is expected to include the development of a corridor plan and upgrades to the Tuggeranong Parkway between the Glenloch Interchange and Cotter Road. It is also likely to include upgrades to feeder intersections and roads like Athlon Drive.

The government will also put $2.5 million into planning and design work for upgrades on Parkes Way. The local government estimates there is $26 million worth of work that could be done on the road to improve capacity and congestion.

With work already under way on upgrades to the Monaro Highway, the federal government will also pledge an extra $15.25 million to the project, for "significant design enhancements" on the work at the Lanyon Drive intersection.

A concept design for that intersection was released earlier this year, and both the federal and ACT governments have put aside $100 million each for upgrades on the busy arterial road.

It's unclear if the extra spending announced on Monday represents a cost blowout or if more elements have been added to the upgrades.

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Ahead of the official announcement, Prime Minister Scott Morrison said an extra $180 million was going into "shovel-ready" projects in the ACT.

"This latest investment will provide another boost to the local economy by supporting an estimated 400 direct and indirect jobs across the territory," he said.

Deputy Prime Minister and Infrastructure Minister Michael McCormack said the government would use local businesses to ensure the projects stimulate the local economy.

ACT Senator Zed Seselja said, "The government's commitment to critical infrastructure continues across the territory, including an $88 million investment for the Molonglo River Bridge, supporting local jobs and businesses at the time it is needed most.

"Upgrades to the the Tuggeranong Parkway and Monaro Highway will make Canberrans' commutes faster and safer."

"I fought hard for this and it builds on over $1 billion in commitments from our government to Canberra just in the last two years," Senator Seselja said.

The two major spending announcements will be good news for the Canberra Liberals, falling in the Murrumbidgee and Brindabella electorates.