Mr Key confirmed government support for three major transport projects on Friday, and the fast-tracking of three smaller highway projects.
But Aucklanders will have to wait until 2020 for construction of the central city rail link, and until 2025 for a new crossing of Waitemata Harbour to alleviate the ageing Auckland Harbour Bridge.
Supporters say the city rail link, which would turn Britomart from a dead-end into a through station, would double the capacity of the rail system, revitalise many parts of the city and allow rail to the airport and the North Shore.
But the government won't fund part of the $2.86-billion project earlier unless city centre employment increases by 25 per cent and rail patronage increases from 11 million trips at present to 20 million.
However, he said those targets could well be met, particularly that for employment, which had been predicted to increase by 50 per cent by 2021.
"That's pretty generous, saying we're expecting it to live up to half the modelling and it'll still start earlier."
Mr Key said a new Waitemata Harbour crossing will be needed between 2025 and 2030 because Auckland Harbour Bridge had limited life.
"It can't take the weight of traffic, it can't take the weight of the trucks and it can't take future congestion."
Mr Key said a greater priority than both was the East-West link between the industrial areas of Onehunga, Mt Wellington and East Tamaki, which was frequently congested with trucks.
Of more immediate priority will be cheaper plans to fast-track three road projects: widening the Southern Motorway between Manukau and Takanini, and improving both State Highway 16 between Upper Harbour Highway and SH1, and SH20A from Auckland Airport to SH20, to motorway standards.
Mr Key said it was necessary to invest in the projects.
"If we don't build them we'll be behind the curve, and long term we'll actually pay for that with lower levels of productivity, lower levels of growth and higher levels of inflation."
