Buses could provide public transport direct to Brisbane Airport after 2014, according to Brisbane City Council.
The restricted timetable of the Airtrain service, which has a virtual monopoly on public transport to and from the airport, has long been an issue for travellers.
The contract between the state Transport Department and the rail provider is confidential and it appears unclear when the monopoly could be broken, with a spokesman for Transport Minister Scott Emerson saying Airtrain had exclusive rights to service the airport until 2036.
However in April 2011, council told the Productivity Commission that a change in the contract to allow the introduction of buses was possible after 2014.
The issue was raised earlier this week by Brisbane Airport Corporation chief executive Julieanne Alroe, who said public transport was becoming more popular among air travellers.
BAC's figures showed the share of people using Airtrain increased from around 6 per cent in 2008 to around 8 per cent in 2011, while a further 13 per cent used private mini-buses and coaches.
Airtrain, a private company, runs the rail link from Eagle Junction to the international and domestic terminals. Its confidential contract with the Transport Department to provide rail services runs until 2036.
Airtrain built the rail link without government assistance at a cost of $200 million and opened the service in 2001.
That was confirmed last night by a spokesman for Mr Emerson, who said the contract ran for 35 years.
"In 2001, the Labor government signed a 35-year agreement with Airtrain that excludes the operation of subsidised public transport buses to Airtrain stations," he said in a statement.
However, council's report to the Productivity Commission appears to contradict this.
"Under the agreement between Airtrain and Queensland Transport, Brisbane City Council is not permitted to operate a bus service within one kilometre of Airtrain stations until 2014," it reads.
"As both the domestic and international terminals fall within one kilometre of an Airtrain station, Council can only provide limited services.
"Though other sources of transport service the Airport, competition appears to be constrained due to factors such as contractual arrangements, restricted hours of operation and limited access."
That is why three state government-subsidised bus services (routes 590, 369 and 303) run by council have to run no closer than the DFO shopping centre near the airport.
Lord Mayor Graham Quirk is in China and his office would not let Deputy Lord Mayor Adrian Schrinner speak on the issue, because the contract parties are the state government and Airtrain.
However a spokesman for Cr Quirk said he believed 2014 was when Airtrain's exclusivity agreement for public transport ended.
"But when it gets to 2014, whether they decide to open it up or not, we would have no idea," he said.
Mr Emerson's spokesman, who also worked at Translink, spoke with three senior departmental officers last night, who said they did not believe changes could happen in 2014, although none remembered the Airtrain contract in detail, he said.
Airtrain now charges $15.50 for a one-way trip between Central Station and the domestic terminal, with 1.5 million people using the service last year.
The same journey could be a zone three Go Card bus trip which would cost $4.24 in peak hour or $3.40 in off peak.
Tourists using a paper ticket would pay $6.30 for the same bus trip, less than half of Airtrain's fare, though again Airtrain services are not subsidised.
Ms Alroe said BAC's research showed that the number of people using private vehicles to get to the airport was declining.
"Using private vehicles particularly to pick up and drop off is one of the declining areas," she said.
"We are certainly seeing shifts to public transport."
BAC statistics for 2011 show that for the domestic terminal: the Airtrain carried 8 per cent of passengers, private vehicles had 50 per cent, taxis had 26 per cent of passengers, while mini-buses had 13 per cent and private limousines had 3 per cent.
Airtrain's chief operating officer Neil Dickin said the company made a $15.7 million profit in 2011- 12, a 25 per cent increase on the 2010-11 profit figure of $12.5 million.
Mr Dickin said Airtrain's contract was for 35 years, but when asked about bus services, he said he "could not go into the details of the contract".
"We have around 1.5 million passengers a year, which equates to around 7 per cent of the patronage at Brisbane Airport," he said.
"It has been steady over the past three years. It stays steady at about the 7 per cent market share."
Mr Dickin repeatedly declined to comment on details within the contract involving bus services to the airport.
In 2009-10 BAC received $840,000 in "landside access charges" from private bus companies (mainly Coachtrans) using the airport.
It also received $140,000 from Airtrain as a train corridor lease, according to council's submission to the Productivity Commission.
It is unclear whether a bus service along the recently opened Airport Link tunnel has been investigated.