Planners of Melbourne’s proposed airport rail look to have a clear choice between two routes: through Sunshine, or through Highpoint and Maribyrnong.

 he Sunshine option could also act as an interchange for regional commuters on the Ballarat and Bendigo lines, offering a more direct route to the airport.

Trains could reach Melbourne Airport from the CBD in as little as 15 minutes, and get travellers from Geelong to Tullamarine in less than 45 minutes, even after stopping at Sunshine, according to a group of experts.

But the Maribyrnong option – understood to be favoured by the federal government, which owns a large tract of development land along the route – could link high growth-rate suburbs in the north-west into the city's rail network, offering "value capture" that could help offset the project's cost.

Value capture is a way of generating revenue from higher property values and other commercial opportunities that would spring from the route of the proposed line.

A third option, a spur between the existing Craigieburn Line and the airport, is now considered unlikely because the suburban line is so heavily used that it would have to be duplicated to allow airport services to run with the required regularity.

The “Albion” option, proposed by Public Transport Victoria in 2012, which would run airport-bound trains on the Sunbury line through Tottenham, Footscray and Sunshine, is also now thought to be impractical due to the strain on the Sunbury line following the population boom in the western suburbs.

John Hearsch of advocacy group Rail Futures Institute, which has been lobbying for airport rail for years, says he and his colleagues firmly believe the Sunshine option is the better of the two contenders.

The rail expert said the Maribrynong route would require more tunnelling than the Sunshine option and was envisaged as a suburban line with several stops that would not allow the speed or frequency of service required for a successful airport link.

“It [Maribrynong] would be part of the suburban system, not a stand-alone railway, so they’d be mixing it with normal suburban passengers, you wouldn’t have a specially dedicated, fitted out train designed for airport passengers,” he said.

“The trip, because of multiple stops, is likely to be slower and the line would suffer all of the day-to-day travails of the suburban system.

“If it’s a suburban service, it won’t be suitable for having connections into the regional network.”

Mr Hearsch said Melbourne airport rail via Sunshine could be on par with the Heathrow Express, which gets travellers from central London to the international air-hub in 15 minutes or Hong Kong’s Airport Express which completes the 35 kilometre trip from the city in just 24 minutes.

But the Turnbull government, which has offered $5 billion to help fund the long-awaited rail line, says it wants all options thoroughly examined in the early planning process currently under way.

Canberra says it is not pushing for any particular route, but that it does want each option to be genuinely considered.

It is understood the Prime Minister’s office wants to share equal control with the Andrews state Labor government in return for Commonwealth financial backing, and may ask for the establishment of a joint federal-state authority to build the railway.

The Commonwealth is paying most of the $40 million cost of the business case, which is due to be completed in September. It will be trying to ensure the study does not become a rubber-stamp for Victoria’s plan to link airport rail with the regional network in the state’s west, making Sunshine the key junction.

The state government wants to run trains directly from Southern Cross to Sunshine and then straight out to the airport. It believes there is an opportunity for an “elegant” solution to link Geelong, Ballarat, Bendigo and eventually Shepparton into the regional rail network.

With Prime Minister Malcolm Turnbull and Premier Daniel Andrews due for a rare face-to-face meeting to discuss the proposed rail line, the preferred route, as well as finance options, look set to be among the key talking points.