New Zealand's largest roading project is weeks away from completion.
The $1.4 billion Waterview Connection - twin 2.5km tunnels and 2.5km of motorway that will provide a second route through Auckland, bypassing the city centre - is set to open in April, most likely the weekend of April 8 and 9.
NZTA Auckland highway manager Brett Gliddon said the only remaining works involved polishing road surfacing, line marking, signage and testing all the electrical tunnel equipment before the route can be used.
When finished the connection would provide the "missing link" between the Southwestern Motorway and SH16. The new route will provide faster more direct transport options and prevent total gridlock if an incident blocks one motorway, he said.
Existing infrastructure is feeling the strain of Auckland's burgeoning population. Since 2013 Auckland has grown by 121,000 people and there are 44,000 more vehicles on Auckland roads than this time last year.
Gliddon said the benefits to Aucklanders would be "huge".
People who live in the north and west will have an alternative route through the city, there will be a full motorway connection to the airport and motorists can bypass the CBD on the Western Ring Route.
Cyclists will also benefit with an upgraded cycleway along the Northwestern motorway and a new cycleway following the Waterview tunnels. Dedicated bus lanes along SH16 will speed up public transport.
"It is going to change travel patterns," Gliddon said.
"A lot of traffic will come off Mt Albert, Sandringham, Mt Eden, Avondale as there's a lot of rat-running that happens through those streets.
This was never about fixing peak time congestion. We were always still going to have morning and afternoon peaks. But it does allow us to rebalance the traffic across the network a lot more efficiently.
Gliddon said the tunnels, 6m to 45m below ground, had state-of-the-art design and safety, with next generation equipment.
"It's a fully automated system. So if a car stops, the cameras pick that up, it comes up on the screen for an operator. If a car catches fire, the deluge system starts.
"There's a PA system and radio override. If you're listening to the radio we can send a message to the radio and tell people what to do."
The current fit-out included compacting 74,500 cubic metres of aggregate for backfill, laying almost 5km of drainage pipes, installing 104 flame traps and applying 140,000sq m of paint: black on the roof so drivers are not distracted and what's above them just disappears, and cream on the walls for high visibility.
The 87m long tunnel boring machine, nicknamed Alice, was designed for the Waterview geology by the German company, Herrenkencht, and manufactured in China.
The public will be able to walk through the tunnels on an open day next month.