Australia’s independent infrastructure advisor has given its seal of approval to boost Melbourne’s Monash Freeway to 10 lanes, giving the green-light to half a billion dollars in federal government cash.

The second stage of the project has been deemed a high priority after Infrastructure Australia approved the business case which aims to help meet the growing demands of Melbourne’s southeast.

Under the plan, freeway lanes would increase from eight to 10 to the west of Eastlink and east of Clyde Road – adding 36km of new lanes, the managed motorway technology would be extended, freeway connections at Beaconsfield would be upgraded and an extension of O’Shea Road in Berwick.

Infrastructure Australia chief executive Philip Davies said the project was a “sound investment” and would complement the works already underway to improve the major arterial.

“Monash Freeway is one of Melbourne’s critical transport links to the south east and outer south east regions, carrying over 470,000 trips per day and providing access to the growing Monash and Dandenong employment centres,” Mr Davies said in a statement on Wednesday.

“Without action to increase capacity on the Monash Freeway, drivers in Melbourne could face slower and less reliable travel times.

“This will worsen as freight and commuter demand grows, particularly where Monash Freeway intersects with the Princes Freeway and at the entry and exit ramps.”

Infrastructure Australia says every $1 spent on the project would give a $4.60 return to taxpayers.

The federal government promised the $500 billion in 2016, but would only give the money if Infrastructure Australia gave the project business case the green-light.

Roads Minister Luke Donnellan told 3AW radio on Wednesday the upgrade would reduce travel times for motorists with construction to start in 2019 and to be finished by 2022.