The ACT wants the NSW and federal governments to commit funding to finding ways to improve rail travel times between Sydney and Canberra.
The territory wants to make improvements as quickly as possible to the existing service rather than waiting for a future high-speed upgrade.
Chief Minister Andrew Barr would commit $5 million to feasibility works if NSW agreed to make the same contribution and the Commonwealth chipped in $10 million.
Mr Barr wrote to NSW Premier Chris Minns in March, seeking the NSW government's support for the jointly-funded project to develop a business case for upgrades.
"I believe that there is currently a strong consensus across ACT, NSW and Commonwealth governments to progress immediate opportunities to deliver improved rail services," Mr Barr wrote.
But the ACT's pitch for Commonwealth funding has so far been unsuccessful, with this week's federal budget revealing no new funding for the Canberra-to-Sydney rail feasibility project.
The territory pitched the $20 million feasibility work to the federal government under the national capital investment framework in September 2023, documents tabled in the Legislative Assembly on Thursday revealed.
The proposal showed a business case for the first stage of priority rail improvements would have been be completed in December 2025 if funding was included in the Commonwealth's December 2023 mid-year economic and fiscal outlook.
"Improving the rail link between Canberra and Sydney is a key priority for the ACT government as a step on the pathway towards high-speed rail. Transport modelling in 2019-20 indicated that travel time improvements could see rail services carry more than 50 per cent of trips between Canberra and Sydney as well as increase the overall number of trips," the proposal said.
The proposal also noted pre-feasibility investigations completed by the NSW and ACT governments between 2018 and 2020 could form the basis for more work.
Mr Barr told Mr Minns he believed high-speed rail should remain the long-term objective but small-scale improvements should not wait.
"Reducing rail journey times between Sydney and Canberra to three hours would see a considerable shift in mode share, travel choice and expand economic activity in the region, however, improvements that achieve a reduction of just 30 minutes would also provide considerable benefit for existing users," Mr Barr wrote on March 9.
"These improvements, which could include express services, increased frequency, reliability and service priority as well as minor track realignments, could be delivered at minimal financial and opportunity costs and would pave the way for multigenerational change."
Mr Minns' office was contacted for comment on Thursday afternoon.
Passenger numbers were up by almost one-third on the Canberra-to-Sydney line in 2023, with 23,700 passengers taking a trip in either direction on average each month. Passenger numbers in the first three months of 2024 were slightly higher than the same period in 2023.
The NSW government is not currently planning additional services on the line, which operates three daily inbound and three outbound services.
But just under 68 per cent of trains on the Canberra line ran on time in 2022-23, down slightly from 73.9 per cent in 2021-22, the operator's annual report shows.
A true high-speed rail link would drive economic wealth in the broader Canberra region by drastically improving the area's connection to Sydney, and could be completed by 2045 if work began on the project immediately, a leading international rail expert said in March last year.
Professor Andrew McNaughton, who prepared a report for the NSW government on the future of rail connections in the state, said that unreleased modelling showed there was a genuine case for high-speed rail between Sydney and Canberra, which would "take off" as a city region.
