Senior ministers have been briefed on the proposal, including Treasurer Tim Pallas and Public Transport Minister Jacinta Allan. Transdev and infrastructure developer John Laing submitted the idea late last month, using the Department of Treasury's market-led proposal guidelines – the same process Transurban used to gain approval for its West Gate Tunnel project. It is estimated the Doncaster-CBD busway would cost more than $500 million to build, which is 10 to 16 per cent of the estimated $3 billion - $5 billion cost of building Doncaster rail, a project Infrastructure Victoria assessed last year would return just 10 cents for every dollar spent. Transdev wants to pave over the Eastern Freeway median – which has been reserved for almost 50 years for a future Doncaster railway line – for express buses instead of trains.

The buses would be double-articulated, with doors on both sides like trains and trams, and big enough to fit up to 150 passengers. They would run every three minutes in the peak and every five to six minutes off-peak. Platform bus stops would have myki readers so buses would not be delayed while passengers touch on and off. New bus "stations" would potentially be built at intersections above the Eastern Freeway, at Chandler Highway, Burke Road and Bulleen Road. This would involve building platforms over the freeway, with escalators and lifts down to road level.

From the Eastern Freeway the busway would join Hoddle Street via a dedicated ramp, then potentially follow Victoria Parade and Lonsdale Street to a new underground bus terminus at the northern end of Southern Cross Station. If the busway followed Lonsdale Street, the trees and on-street car parks in the median would be replaced by bus lanes and platform stops. Express bus lanes would also be built in the centre of Doncaster Road, running from the current park and ride bus terminus, which would be expanded with a new underground car park, to a new bus terminus at Donvale Hospital. Other vehicles such as cars and trucks would be strictly banned from the busway.

Modelling by engineering consultancy AECOM found the bus rapid transit system would provide a reliable 30-minute journey between Doncaster and Southern Cross station. Currently that journey takes 47 minutes or more in the peak due to inner-city traffic jams. AECOM forecast the service would be used by 24,000 people in the combined morning and afternoon peaks, roughly eight times more than use the current Doncaster bus routes to the city. Transdev argues its busway would be more like a railway, with superior travel speeds and service consistency, than a conventional bus route. The busway would not preclude future construction of Doncaster rail in the freeway median.

The concept has already won the support of the Eastern Transport Coalition, a group of seven eastern suburbs councils pushing for better transport in Melbourne's east. The Coalition said traffic congestion on Hoddle Street, Lonsdale Street and at the end of the Eastern Freeway "compromises travel time" for Doncaster buses, which are the only public transport between Manningham and the city. It endorsed a bus rapid transit system in its Commuters Count campaign, launched this week. Monash University's Professor Graham Currie helped to design Melbourne's current SmartBus network and said many cities had chosen bus rapid transit systems as an effective and less expensive alternative to rail. "It's a rubber-tyred railway, the new technology dominating public transport thinking on planet Earth," he said of the concept.

Brisbane has an established rapid transit bus network. Credit:Glenn Hunt He said Victoria had only made half-hearted attempts at bus priority and it was time to get serious. "People have a negative view of buses because they are in mixed traffic, because they are infrequent, unreliable – you don't have to run buses that way at all," he said. But he questioned the need to use the Eastern Freeway median, arguing the biggest issue for the current Doncaster bus services was congestion in the inner city. Daniel Bowen, spokesman for the Public Transport Users Association, said the busway would be "a quantum leap over the current bus service" in terms of capacity and reliability, but would never match the capacity of heavy rail.

"Many people would still want Doncaster rail to be built," Mr Bowen said. With a proposed capacity of 150 passengers, the buses would fit three-quarters as many passengers as an E-Class tram, the largest tram type in Melbourne. Transdev spokeswoman Kathy Lazanas said the proposal put to Treasury last month would evolve through consultation with the community, should the Andrews government support it. "We will work with the Victorian government through its well established market-led proposal process," Ms Lazanas said. The guidelines state all private sector proposals put to the government must be unique.