Rail to Auckland Airport is going back to the drawing board as transport planners consider trams as a cheaper option.

Auckland Transport is under pressure to safeguard a rail route from Onehunga to the airport before the NZ Transport Agency builds a $140 million motorway extension along George Bolt Drive - some of it in a trench below Kirkbride Rd in Mangere - from early next year to 2017.

Electric trains were the preferred option of a multi-agency group led by the council body in 2011, after Auckland Mayor Len Brown promised airport rail by 2020 in his first Super City election campaign.

It was to be his second transport priority after the $2.4 billion rail loop under central Auckland. But airport rail slipped down the list in 2012, in favour of a new road link from Onehunga to East Tamaki, and 2030 was reset as the target for a $1.18 billion loop through both Onehunga and Manukau.


The cost estimate has since ballooned to $1.63 billion for just one link by 2045 as an extension of the Onehunga railway line. Even that depends on alternative revenue such as motorway tolls or higher fuel taxes and rates being provided to fill a $12 billion transport funding gap.

The new estimate appears to have prompted Auckland Transport to reconsider light rail - or trams - to the airport to cut costs even though the multi-agency group rejected it.

"Light rail would provide more opportunities to route the track in a way that reduces the infrastructure cost," a spokesman told the Herald.

"A light rail corridor could be routed in a way that removes substantial costs associated with placing heavy rail in a trench."

The development has dismayed Mike Lee, Auckland Council's infrastructure committee chairman, who chaired the multi-agency group, as well as the Campaign for Better Transport, which sponsored a 10,000-signature petition in 2007 calling for airport rail.

Mr Brown noted from China last night the group's support for trains to the airport as the best long-term solution and said: "Aucklanders would need to be convinced any other option would stack up." But a route should be "future-proofed" for either option.

Mr Lee said light rail was suitable for inner-city transit but not for long-haul work. "Unless you're going to build 23km of new tram tracks winding through the suburbs, passengers would have to disembark [with their] baggage at Onehunga to wait for a train."

Cameron Pitches of the Campaign for Better Transport said it was frustrating costs were climbing as land was being built on rapidly in the path of a potential rail route.