A commuter rail link to Auckland Airport - which could slash travel times to the international gateway - has been dumped in favour of trams or buses.

LISTEN ABOVE: Matt Lowrie, editor of transportblog.co.nz, talks to Larry Williams

The scrapping of the heavy rail connection is a U-turn by the New Zealand Transport Agency, which last year said it was "extremely committed to providing a rail link connecting the airport and the city".

Auckland Transport (AT), which has favoured rail to the airport as a high priority, meets today to decide if it will endorse the agency's position.

Road travel typically takes about an hour from the city centre to the airport. Commuter rail could cover the 20km journey in 35 minutes.

The Transport Agency's board ruled out heavy rail after it was shown an AT report at its last meeting.

Agency regional director Ernst Zollner confirmed further investigations for rapid transit connecting the city to Mangere would be limited to light rail or a busway.

"This is based on evidence from Auckland Transport that a heavy rail option to the airport would present poor value for money."

The same report is to be presented to the AT board today in a session closed to the public. The meeting's agenda lists the reason for privacy as commercial sensitivity.

An AT spokeswoman expected the report to be made publicly available shortly after the meeting.

Campaign for Better Transport convenor Cameron Pitches, who has been pushing for rail to the airport for more than a decade, said he has now given up on it ever happening.

He said it was the only sensible option and did not think the business case for trams took into account the cost for new stations and works necessary to complete the network.

The addition of a busway as an option was also new to Mr Pitches, who said the project needed greater transparency.

"It's all very mysterious how transport decisions get made."

Auckland Council infrastructure chairman Mike Lee, who heads a steering group of parties including KiwiRail considering rapid transit options for the airport, said he believed the imminent removal of the Neilson St overbridge at Onehunga would compromise the possibility of protecting the route for rail.

Removing the overpass was extremely short-sighted, he said, because a rail overbridge would need to then be built to allow for commuter rail, adding significant costs.

"The other odious aspect to this is NZTA suggesting they support light rail to the airport and foreclosing on conventional rail while conspicuously refusing to endorse light rail on the isthmus. Auckland taxpayers and ratepayers deserve better than this nonsense."

The transport bodies are under pressure from Auckland Airport to make a decision by August when the company needs to know what form of rapid transit to include in its plans to build a new domestic terminal to by 2021 and a second runway a few years later.