Travel on Victoria's trains, trams and buses became free from Tuesday until the end of April.
The fare reprieve is designed to take pressure off motorists at the petrol pump, encouraging people to ditch their cars and reduce demand for fuel.
But the initiative is causing headaches for some commuters, who fear services will be swamped.
Portland grandmother Wendy Taylor worries she won't be able to find a seat on the train to Geelong for an upcoming medical appointment.
For the month, seat reservations are not available on long distance V/Line services, meaning it is a matter of first-come-first-served.
While the state government said existing seat reservations will be honoured, Ms Taylor fears hers might be lost in the rush.
"I'd much rather just pay for it and you're guaranteed a seat," she told AAP.
"I just think it will be a dog's breakfast."
Rather than risk not finding a seat on the train to Melbourne, Warrnambool local David Colson plans to drive to his doctor's visit.
"The irony is they're tying to put less strain on fuel, but I'll be driving myself when normally I'd be getting the train," Mr Colson said.
"It's a bit different to be standing on the way home from Collingwood to Heidelberg than it is for three hours on the train to Warrnambool."
No additional services have been allocated for April, but Premier Jacinta Allan said the transport network is well-placed to handle it.
"We have a strong public transport system because we've literally built it," she told reporters on Tuesday.
The state Labor government will monitor the number of people using public transport to guide whether additional services are needed, she said.
But many believe overcrowding is a matter of when, not if.
"There are some areas of Melbourne and Victoria where trains, trams and buses are already quite crowded," Public Transport Users Association spokesperson Daniel Bowen said.
"The government should be planning to deploy more services where they can."
Buses will replace trains for sections of the Warrnambool and Geelong lines from April 11 to 24.
South-West Coast MP Roma Britnell said she had been raising the issue of unsafe overcrowding on V/Line services with the public transport minister for months.
"The lack of understanding from this government is gobsmacking," the Liberal MP said.
Victoria's move is expected to cost $71 million in lost revenue but Ms Allan said a regular public transport user would save $228 over the month.
Tasmania is the only other state to have rolled out free transport, with buses and ferries free from Monday until July 1.
Western Australia, Queensland and NSW have indicated they won't follow suit.
"There's no such thing as free public transport," NSW Premier Chris Minns told ABC TV.
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