Bridges said what could swing it for National is more work being done by Auckland Transport and the New Zealand Transport Agency into the best option - buses or trams - costing up to $1.2 billion.
Auckland Transport said the cost for light rail from the CBD, via Mt Roskill, to the airport is $2.5b to $3b. Labour has costed light rail from the CBD to West Auckland at $2b.
The need for a mass transit solution from the CBD to Mt Roskill has been brought forward in a joint, 30-year transport programme between Auckland Council and the Government.
Population projections suggest 100,000 more people will be living in Auckland by 2026, bringing the population to 1.9m people.
Bridges said National was prioritising other projects in the 'Auckland Transport Alignment Project' work programme, including a new $995m highway alongside the Southern Motorway between Manukau and Drury. Labour's Auckland Issues spokesman Phil Twyford said he suspected National was warming to light rail in proportion to their polling numbers going down.
"We need a modern transit system for the city and it has taken years for the National Party to get their head around that," Twyford said.