Auckland Transport is considering running trams to the airport via Dominion Rd, one of the Super City's busiest commuter routes.
Its consultants have nominated 20 potential tram stops between the airport and Britomart - including eight along Dominion Rd and four on Queen St - but questions are being raised about how the route could serve both long-distance travellers and commuters.
An estimated journey time of 44 minutes for the 21km trip is seen as optimistic by the Campaign for Better Transport and Auckland Council infrastructure chairman Mike Lee, who heads a steering group of parties including KiwiRail considering "rapid transit" options for the airport.
That time assumes trams would travel at up to 80km/h and compares with about 39 minutes for 110km/h electric trains or up to an hour for buses jostling with other traffic.
Transport campaign spokesman Graeme Easte, an Albert-Eden Local Board member, said yesterday that he feared commuters on what was now a very convenient and frequent-service bus route would lose out.
"People wanting to get home at rush hour will be tripping over people with luggage, large packs and the odd surfboard," he said.
Mr Lee said he had reservations about the effectiveness of a longer-distance rapid transit airport service using Dominion Rd and was sceptical about some of the numbers and assumptions in a report by the consultants.
He believed there was "a major flaw" in business case comparisons estimating the cost of extending trains to the airport at $2.3 billion compared with $1.1 billion for trams.
That was because electric rail already ran to Onehunga - just 10km from the airport - yet a tram line via Dominion Rd "exists only in the imagination at this stage".
Mr Easte said he understood the light-rail estimate was on top of whatever it would cost to run tram lines along Dominion Rd to Denbigh Ave, from where they would turn east to follow the Southwestern Motorway to the airport.