Passengers have launched a petition to try and save the rail service that passes through Murray Bridge after its state government funding was pulled last week.
Almost 800 people have so far signed the petition to save the Overland, which runs twice per week between Adelaide and Melbourne.
It was started by Melbourne resident Steve Bayer, who argued that alternative modes of transport "will not be able to cope" with the overflow, and that those with mobility issues would find it harder to board coaches or airliners.
Petitioners also worried about the lack of alternative transport in regional areas and the increased burden that would be placed on roads and, by extension, the environment.
Several said they would be more likely to take the train if it became an overnight service once again, as it was from 1887 until 2007.
A South Australian government subsidy for the service will cease at the end of December, reportedly because passenger numbers are too low and alternative transport options are available to regional residents.
In a statement, operators Great Southern Rail (GSR) said subsidies from the SA and Victorian governments were what kept the Overland affordable, and therefore commercially viable.
"Our intention is to advise regular patrons what is happening with the service so they can make informed travel decisions for the future," GSR said.
"Having now received the South Australian government's advice, Great Southern Rail has started to explore any opportunities available to provide a short-term transitional travel phase beyond December."
The last train for which bookings are still being taken will depart on December 31.
Opposition transport spokesman Tom Koutsantonis called on the state government to reconsider its decision.
"This is a vital service, particularly for older South Australians who prefer train travel, and for country South Australians who do not live close to airports," he said.
Victoria had pledged in August to give the Overland a 15-month lifeline, but the federal government stopped funding the service in 2016.
The Overland was originally an overnight service which operated every 24 hours.
Its frequency was reduced to five nights a week in 1998, less than a year after the national railways were privatised.
Services were further cut back to four per week in 2000, then three daylight trips in 2007 and finally two in 2013.
GSR did not respond to a request for further comment.
- Sign the petition: www.change.org.au.