The funding and ownership deal was signed at the Henderson railway station yesterday by Transport Minister Steven Joyce and Auckland Mayor Len Brown, after they arrived there together by train.
It is to be sweetened further by a separate Government grant of $90 million to ensure enough trains can be bought under a supply and maintenance contract expected to be signed by the end of this month.
The board of council subsidiary Auckland Transport has yet to make a recommendation between two short-listed suppliers, a consortium led by Spanish company CAF and the South Korean firm of Hyundai Rotem.
KiwiRail, which is buying the trains, has also written a 12-year maintenance period into its requirements.
Mr Brown disclosed that the city may end up having to pay an extra $20 million to $30 million for the trains, on top of the Government's grant, a difference which may point to a fine balance between the competing bids.
But he said Auckland had initially expected to pay for the trains by itself, through a regional fuel tax since blocked by the Government. "Under this deal, Auckland Council and NZTA [the Transport Agency] will split the loan repayments."
Mr Joyce said favourable international trading conditions were enabling the purchase of the extra trains with "probably less of a stretch than we previously thought".
A "single homogenous fleet right through the city" would cost less to operate than a mixed bag of trains.
"That was one of the things we were all troubled with in terms of the operating deficits apparent.
"And it really does set a much better customer experience," he said.
The multiple unit electric trains will be considerably faster than those hauled by locomotives, which take longer braking into stations and accelerating out of them.
THE DEAL
* $500 million: Government loan to KiwiRail that Auckland Council is to take responsibility for
* $17 million: average annual cost to Auckland ratepayers
* 57: three-car electric multiple unit (EMU) trains, a depot and 12 years of maintenance is what the deal will buy