Existing commuters have to change trains at Newmarket when travelling from south to west, and at Papakura when travelling to and from Pukekohe.
However, an Auckland Transport spokesman said the diesel trains did not meet fire safety standards to use the Waitakere tunnel and it would cost millions of dollars to bring the tunnel and trains up to scratch.
He said Auckland Transport, New Zealand Transport Agency and Auckland Council were working through the best transport options for the Whenuapai, Red Hills, Riverhead, Kumeu and Huapai areas.
"We have considered improvements to the rail network and tying into the proposed busway along SH16 from Westgate to the CBD and SH18 from Westgate to Albany.
"The extension of the busway along SH16 and SH18 would provide public transport to the employment centres on the North Shore and to the CBD within about 45 to 55 minutes.
"The rail network is a single line to Swanson so it would also take significantly longer to get to the CBD and would probably only be able to provide an hourly service from Huapai to Swanson," the spokesman said.