Night-time traffic on Auckland's Northwestern Motorway is being diverted as heavy concrete beams are lifted into place for a giant triple-level traffic interchange at Waterview.

Closures of the motorway's westbound lanes are taking place late each night this week, when traffic is lightest.

Those are to be followed by closures of eastbound lanes next week, as the second of four traffic ramps for the new interchange is extended over the northern side of the motorway as part of the Transport Agency's half-tunnelled $1.4 billion Waterview Connection link.

The beams, up to 36 metres long and weighing between 60 and 69 tonnes, are being lifted by a large yellow gantry which has already completed the first ramp needed to carry traffic from central Auckland to a motorway tunnel being dug from Mt Albert. The second ramp now being erected will carry traffic from the west to the tunnel.


Transport Agency highways manager Brett Gliddon says the gantry eliminates need for conventional cranes which would have had to be moved into place at the start of each work shift and then taken away again before morning traffic peaks.

"It saves time, reduces traffic disruption and avoids the need to use those cranes in the environmentally sensitive areas of the Oakley Creek estuary," he said.

Although the gantry remains perched above the motorway by day, Mr Gliddon assures motorists it is not working over "live" traffic lanes.

A large boring machine has meanwhile completed about 70 per cent of a 2.4-kilometre underground journey from Alan Wood Reserve in Mt Albert to Waterview, ready to hole through next to the suburb's primary school late next month or in October.

It will then be turned around to dig the second of two tunnels expected to open in early 2017 to connect the Northwestern and Southwestern motorways, allowing faster trips to and from Auckland Airport.