Foreign Minister Julie Bishop will join member for Eden-Monaro Peter Hendy to announce the spending plan on Sunday in a decision hoped to shore up Dr Hendy's position in the bellwether seat.

The four-year funding commitment, labelled the Barton Highway Duplication Package, does not guarantee a full duplication of the two-lane stretch of the highway, but provides $45 million for overtaking lanes which would extend the future corridor.

Another $1.75 million would go to a duplication business case which would include recommended staging and costings for the highway duplication.

The remaining $3.25 million would be spent on safety upgrades, including so-called intelligent transport systems which use real-time traffic monitoring, CCTV and electronic signage to inform motorists about traffic conditions and better manage accidents.

"This $50 million package will secure upgrades to the Barton Highway, focusing on the southern and central sections of the highway where traffic volumes and safety concerns are paramount," Ms Bishop said.

"We are focused on delivering a package which will provide a better Barton Highway in both the short and long term, delivering much needed upgrades which progress the staged duplication of the highway."

Dr Hendy said the safety improvements, particularly overtaking lanes in the worst sections of the road, were the "next step in the staged duplication" of the highway, but were "done with one eye firmly on acquiring the ultimate duplication corridor".

No specific construction timeframes or locations were provided, with these and the overall distance covered by the extra overtaking lanes understood to be decided in future project development and through the strategic business case.

Labor's candidate and former Eden-Monaro MP Mike Kelly hinted at an opposition announcement last Wednesday, where he attended the launch of a campaign by the unaligned Barton Highway Community Action Group who called for the issue to be high on the agenda for voters on July 2.

"I'm working on this at the moment, and we'll have more to say about it later," Dr Kelly said then.

A report published by the federal and NSW governments last year said there had been 137 crashes on the Barton Highway between 2009 and 2013, with seven fatalities and 70 crashes involving injury, with most crashes between Murrumbateman village and the ACT border.

The highway became part of the redrawn electorate this year in changes which nominally increased Dr Hendy's sliver-thin margin to an estimated 2.6 per cent.

Barton Highway roundabout signal build passes half-way mark

The Barton Highway roundabout upgrade at Gold Creek has passed the half way point, with traffic lights to appear at the danger-spot from August.

The ACT government's $10 million project to improve Canberra's most dangerous roundabout adds an additional lane to the four approaches and will install nine sets of traffic lights.

A spokeswoman for Territory and Municipal Services Minister Meegan Fitzharris said recently completed works included the widening of the circulation lanes of the roundabout, which included reducing the size of the roundabout island.

Three approach lanes were also now in place for both the Gundaroo Drive westbound approach and the Barton Highway northbound approach after widening.

"Installation of traffic signals at the expanded intersection is expected to commence in August and work is on track for completion in late 2016," she said.

Liberals roads spokesman Alistair Coe said the opposition's alternative project to build a flyover would begin in the first year of government if they were elected in October.

"The [proposed] flyover bypasses the roundabout, so there will still be a need for an intersection underneath," he said. "The removal of traffic taken by the flyover will make the remaining roundabout function more smoothly."

Speaking before the federal government's $50 million announcement for extra Barton Highway overtaking lanes, Mr Coe said any work on the highway would increase the need to fix the roundabout bottleneck. The ACT government has criticised the price of the flyover plans, which the Liberals have said would cost $35 million.

NRMA ACT director Kate Lundy said last year figures on the capital's worst crash intersections backed the Canberra Liberals' argument for a flyover. Data showed there were more than 500 crashes at the Barton Highway-Gundaroo Drive-William Slim Drive roundabout in the previous five years, making it by far the most common ACT site for a crash.

Congestion and delays caused by the construction have been criticised by some road users.

"If you are going to disrupt services to that many people for a year you would expect roadworks that would deliver a strategic advantage, such as an overpass or underpass, not just traffic lights," Sophie Wade of the Duplicate the Barton Highway Community Action Group said in March.