One of the Government's new roads of national significance is set to be the most expensive ever built anywhere in the world.

Infrastructure New Zealand has calculated Auckland's proposed East West Link will cost $327 million per kilometre.

"It's an enormous amount of money on a very short link of dubious value that does a great deal of destruction to the natural environment," Greater Auckland author Patrick Reynolds says.

It's an arterial road linking State Highway One at Sylvia Park to State Highway 20, estimated to cost $1.8 billion.

Infrastructure New Zealand came up with the comparison but says while expensive, it will be worth it.

"Very important," Infrastructure New Zealand chief executive Stephen Selwood says. "We have another million people coming to Auckland by 2050 we really need to be getting on with providing transport infrastructure needed to support the cities growth."

National backed the plan last month, adding it to its roads of national significance, and promised it would be built if it's re-elected.

"It's not going to be paved in caviar," Prime Minister Bill English says, a nod to the road Vladimir Putin had built for the Sochi Winter Olympics.

The Russian road was mired in corruption and labelled so expensive it could've been paved in caviar or truffle.

"It'll be good old tar seal… and have lots of trucks on it because the economy is growing and busy."

New Zealand Transport Agency's Auckland highway manager Brett Gliddon agrees, saying that comparison is completely unfair because the project has to take into account the harbour, the environmental impact and the local community.

"We picked this option because we thought it was great balance between what the community were wanting and the freight operators wanted and it's much more than just a road."

A cycle and walkway, as well as a beach, will also be built.

A board of enquiry is considering public feedback and will release a decision on the project's fate in November. However it could be killed off before then if the National Party lose on Saturday.

Newshub.