The Sunshine route for an airport train has been given the thumbs up by planners and engineers. Credit:Paul Jeffers The announcement drew immediate ridicule from the Opposition, which produced a 1999 Labor pledge for a "rapid transit link" to the airport. "This isn't an announcement, it's a media stunt," Opposition public transport spokesman David Davis said of Thursday's announcement. But Mr Andrews said that "planning has already begun" on the rail link, which had "the potential to unlock western and northern Victoria".

"It can create the extra capacity that we need in the congested rail corridor between Melbourne and Sunshine," he said. While the government released scant detail of its planning work, the information that has emerged mirrors a proposal by Rail Futures, a group of respected transport engineers and planners. In May the group released its plan for an airport rail line via Sunshine that would see regional trains, including those to Bendigo, running via the airport. Rail Futures president John Hearsch, an experienced rail industry consultant, said an airport rail link needed to get from the CBD within 15 minutes. It also had to be very reliable, separated from the suburban network, and "well and truly future proof".

Melbourne's rapid population growth at its fringes is placing immense pressure on the city's regional trains. The Regional Rail Link, a new line through Melbourne's west for regional trains, opened in 2015. It connected some of Australia's fastest growing suburbs to the rail system and turned the Geelong line into a "pseudo-suburban service" with increased overcrowding and slower journey times. The Regional Rail Link's two suburban stations in Tarneit and Wyndham Vale already carry almost half the Geelong line's passengers, despite opening only two years ago. Mr Andrews said in his speech to the Victorian Chamber of Commerce and Industry that an airport rail link would untangle Geelong and Ballarat line trains from the metro network.

He also said it would enable the electrification of services to Melbourne's western suburbs. This would mean electrifying the Regional Rail Link – which runs only diesel trains – as far as Wyndham Vale and building a new pair of tracks alongside it for express Geelong trains. Similarly it would mean electrifying the Ballarat line to Melton or even Bacchus Marsh and building separate tracks for Ballarat trains. Paul Westcott, the Public Transport Users Association's Geelong convener, said Geelong passengers "think they've been dudded" by the Regional Rail Link. "Overcrowding has been exacerbated by Geelong lines having to become pseudo metro trains," he said.

Similar problems had emerged on the Ballarat line since Caroline Springs station opened in January, he said. Mr Westcott described the premier's announcement as a sketch for planners to get started on. "He's sketched what he'd like but there's certainly nothing much on paper," he said. The Turnbull government has pitched in $30 million for a business case for the airport rail link, and will spend $15 million this financial year. Federal Urban Infrastructure Minister Paul Fletcher said the investigation would "identify and assess a number of potential alignments, some of which have been considered before, including an alignment through Sunshine". A meeting was held at Melbourne Airport on Wednesday of state and federal transport ministers, rail operators and SkyBus and councils. Also present was pension fund giant IFM Investors, which owns almost a quarter of Melbourne Airport. It has previously been reported as wanting to partner with the Victorian government to build the rail link.

Also at the meeting was Peter O'Brien, a consultant who has been lobbying for an airport rail line for several years. He was highly critical of the state government's regional rail push for the airport link. He predicted little would occur as a result of this week's announcement. Loading "It's going to be a frankly very timid effort for the next 12 months - people don't want to progress this at all," he said. In December, Infrastructure Victoria said a rail link to Melbourne Airport would be needed within the next 15 to 30 years.