Six months from completion, Auckland's Waterview tunnel project is close to being finished.

One hundred and forty thousand pots of paint, 4000 light bulbs and five Olympic-sized swimming pools of water - everything about Auckland's Waterview tunnel is big.

New Zealand's longest tunnel and motorway project - the $1.6 billion Waterview Connection - is getting its final fit-out before its opening in early 2017.

The tunnels themselves are curved and on a gradient. They sit about 11m apart, 40m below the surface and are 2.4km long.

Lawrence Smith The completed tunnels will each hold three lanes of traffic.

Eventually they will take three lanes of traffic each.

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​They are connected by 18 cross passages so people can move freely between the two in case of emergencies.

LAWRENCE SMITH / FAIRFAX NZ The tunnels will connect Auckland's northwestern and southwestern motorways.

And speaking of emergencies, the tunnel is able to self regulate. If the thermal sensors detect massive amounts of heat, they will activate the sprinklers.

The "deluge" sprinkler system contains 1250sqm of water - that's five Olympic-sized swimming pools worth.

The tunnels are the last piece in the Western Ring Route puzzle, which will connect the northwestern and southwestern motorways and reduce inner city traffic.

Lawrence Smith The Waterview Connection is New Zealand's longest tunnel and motorway project.

New Zealand Transport Agency highway manager Brett Gliddon said people would not understand the significance of the project until they get the chance to drive through.

"It's just a massive piece of infrastructure - from an engineering perspective, it's just so fantastic to be involved in a project like this," he said.

"There is no other tunnel like this in the country. It's going to be a real eye opener, especially for Aucklanders, because all the tunnels that we have in Auckland at the moment are significantly shorter.

"The closest thing we have to it in New Zealand is the Lyttleton tunnel, which is just under 2km long ... and this is 2.5km long on a grade with a bend."