Lobby groups in Melbourne’s west are now warning this would be disastrous for commuters in the city’s fastest-growing region, who are already being squeezed on to overcrowded and infrequent V/Line services. They say airport trains would clog any spare capacity in the Metro Tunnel for extra Sunbury and Melton trains, while Wyndham Vale services would also suffer. Loading The state and federal governments have each pledged $5 billion for the airport rail project, which is set to open in 2027. A private consortium has offered to chip in $5 billion to build a 7-kilometre tunnel from Southern Cross to West Footscray. In a bid to reduce project costs and get an airport rail link built fast, the federal and state governments appear to be reviving an old plan to run airport trains through the Metro Tunnel – an option that was ditched by state rail planners in 2016.

The 2016 Metro Tunnel business case rejected a 2012 Public Transport Victoria plan to run six airport trains an hour through the Metro Tunnel. This decision was made to create space for an extra three Melton services and two Sunbury services an hour through the tunnel, in the wake of runaway growth in Melbourne's west and north-west. Loading All up, Melton would get nine services an hour and Sunbury would have 14. The Metro Tunnel would have a maximum capacity of 23 trains an hour, leaving no room for airport trains. Future links to Melbourne Airport and Rowville could be possible as part of the Metro Tunnel, the business case found, but these options would require “a complete new network (likely including long tunnels back to central Melbourne) rather than making use of existing tracks".

The current proposal to run airport trains along existing tracks and via the new Metro Tunnel would reduce the number of Melton or Sunbury trains, with Melton believed to be more likely. The Rail Futures Institute estimates that by the time the Metro Tunnel opens in 2025, Melton would probably end up with just three trains an hour – or one every 20 minutes – which is no different from the current situation. This could be increased down the track to six services an hour, once the tunnel is at full capacity. Loading But Melton will need 10 trains an hour by the early 2030s, the experts say, with the Ballarat corridor (which includes Melton) set to service an extra 300,000 people in 16 years' time.

Chief executive of Committee for Ballarat, Michael Poulton, said the airport rail tunnel would disentangle Ballarat and Melton train lines, giving more services to Melton. “This is not political for us, it’s a logical solution to say if you want to free up capacity, that has to be delivered to Melbourne’s west and you have to take regional rail off the current suburban network,” Mr Poulton said. “There are three new railway stations on the Ballarat line to Melton which has slowed the line down … its standing room only.” Loading Meanwhile, the Committee for Wyndham is warning that desperately needed services to Wyndham Vale would not be possible without a fifth and sixth track between the city and Sunshine.

Chief executive Barbara McLure said the airport rail tunnel would enable fast trains to Geelong, which was promised by the state and federal governments before their respective elections. Feeding Geelong trains through an airport rail tunnel would also free up capacity for more Wyndham Vale services to the city. “We’ve got to build for the future,” Ms McLure said. “We are not getting good rail services now.” Loading An airport rail tunnel is understood to have been favoured over a sky rail option, as the raised rail line would have to be built some 20-metres high, over a series of bridges through Footscray and North Melbourne.