Catching the train is becoming so much more popular in Auckland that the city rail link (CRL) could reach capacity within a decade of opening.
The Government and Council are looking at spending hundreds of millions to enable the use of longer trains and avoid more expensive retrofitting later on.
The new projections estimate the stations will need to cope with 54,000 passengers per hour instead of the previous estimates of 36,000.
Transport Minister Phil Twyford says he "totally agrees" with the principle but needs to get Cabinet sign off before committing to increased spending.
"It's an issue of planning properly so that a $3b piece of transport infrastructure that will double the carrying capacity of the existing rail network is actually fit for purpose and doesn't exceed its capacity to carry passengers within 10 years of being completed ," Mr Twyford said on Tuesday.
Auckland Mayor Phil Goff believes the best solution would be building stations that can take nine-carriage trains rather than six and a second Beresford Square entrance at the Karangahape Road Station.
"The time to make the decision on expanding station size is now, not trying to retrofit stations in a decade which will be disruptive and much more costly."
"Preliminary costings suggest doing it at the start may be roughly half the cost of doing it later," Mr Goff said.
The expansion is likely to have support from the Opposition too.
National's transport spokesperson Jami-Lee Ross told Newshub he believes it's "reasonable" for council and Government to look at future capacity.
"The Government and Council do have an obligation to taxpayers and ratepayers to constrain costs and being sure they are being as careful with taxpayers and ratepayers money as they can, but they also have an obligation to ensure the city rail link operates well," Mr Ross said.
"If there's new information that shows the city rail link will be at capacity relatively soon after opening because there is a greater uptake in public transport... that's a good thing."
The CRL will cost an estimated $3.4 billion to build, with the cost shared 50:50 between Auckland Council and Government.