A lack of transport options at Brisbane Airport will be further exposed when the city's new $1.3 billion parallel runway leads to a doubling in passenger movements in 20 years, Brisbane's development association has warned.

Committee for Brisbane executive director Annie Macnaughton said while the new airport facilities would be a boon for the city, accessible public transport was the "missing piece of the new airport jigsaw".

She said those improvements were needed, as the airport's passenger numbers would increase from 23.4 million in the 2018-19 financial year to more than 50 million by 2040.

"I think efficient, fast, 'turn up and go' mass transit in and out of the airport precinct is absolutely essential for Brisbane," Ms Macnaughton said.

The privately owned Airtrain has monopoly access to provide public transport to Brisbane's domestic and international terminals until 2036, due to a contract signed with the Queensland government in 1999. After 2036, the line returns to Queensland Rail.

It was a situation Robert Dow, a spokesman for transport lobby group Rail Back on Track, said needed to change.

"I think there is a need to look at opening it up to normal route public transport in and out of the airport," Mr Dow said.

Lord mayor Adrian Schrinner has asked the state government to revisit Airtrain's exclusivity, floating the idea to have the council's Brisbane Metro buses service the airport.

In addition to passengers, 25,000 people work at the Brisbane Airport precinct - a number predicted to grow to 50,000 by 2040.

As part of the Airtrain contract, the council's buses can only enter the airport precinct as far as the Skygate retail centre, several kilometres from the terminals.

From Skygate, bus passengers catch a shuttle bus to the domestic or international terminals.

"Airtrain expects to provide a complimentary service to the Brisbane Metro when it commences operations because there will be connections between Airtrain and the metro at both South Brisbane's Cultural Centre and the Roma Street stations," said Airtrain chief executive Chris Basche.