Election 2023: Greens promise light rail in Auckland, Wellington and Christchurch within a decade

The Greens are promising light rail for our three biggest cities as part of its new Climate-Safe Communities Plan. But new roads would be kicked to the curb.

Light rail in Auckland Wellington and Christchurch within a decade - that's the Green Party's grand transport plan.

In Auckland, phase 1 would see Britomart to Mount Roskill by 2028, then expanded to the airport by 2032.

In Wellington, light rail from the Railway Station to Island Bay would be operational by 2029.

And Christchurch would be built in two phases, operational by 2032.

"Imagine jumping on fast light rail to get to work instead of crawling along grid-locked roads," said Green Party co-leader James Shaw.

It's about $12.5 billion. Half of it would be borrowed and the rest saved by building Auckland's light rail at street level instead of Labour's $14 billion partially-tunnelled proposal from the CBD to the airport.

"For the price of that, we can build light rail in Auckland and Wellington and Christchurch," Shaw said.

But Auckland's City Rail Link is a prime example of how costs can blow out. The Infrastructure Commission's latest review of the City Rail Link said while it will no doubt deliver significant benefits to Auckland, it's expected to cost more than double what was estimated in 2015 with many billions more to be spent across the rail network in years to come to realise the full design capacity of the project.

"We accounted for currency, we accounted for inflation, and then we added 40 percent contingency," Shaw said.

So, from an economist's point of view, how realistic is all of this?

"There's a lot to be worked out, I think, in terms of how we'd actually build our workforce to be able to do a major project like this without creating extra cost pressures," Cognitus Economic Insight principal economist Richard Meade said.

The Greens would reallocate a billion dollars from state highway improvements to walking and cycling.

"National and Labour have put out plans. Both of their plans would increase congestion and increase road traffic," Shaw said.

But councils would get a new Urban Nature Fund to help prevent future flood events.

"Whether a $750 million spend on extra sponge elements of a city will be enough, I think there's a lot to be debated there," Meade said.

"What kind of world we can create, is all about people and people can change the systems that we live in," Shaw said.

But people have to pay for it too.