Traffic on Auckland's Northwestern motorway is heavily backed up near the Waterview Tunnel - but it's not the tunnel's fault.

The brand-new underground route has been flowing freely in both directions during the evening rush hour.

But a crash further down the NorthWestern motorway caused major congestion with westbound traffic backing up from St Lukes through to Lincoln Rd.

A motorbike and a car crashed between the Te Atatu and Lincoln Rd exits around 4.45pm.

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The crash has since been cleared from the road and heavy traffic was beginning to ease around 6.45pm, the NZTA said.

During this morning's rush hour the Waterview route was incident-free, with many commuters crowing that the new route cut their travel time in half.

Commuters so far have been mostly pleased with the twin tunnels, which have made travel faster both above and below ground by reducing traffic on local streets.

Transport authorities were reluctant to make early predictions about the exact impact of the new Waterview Tunnel, but this morning they praised motorists for the hassle-free rush hour.

Nearly 80,000 motorists drove through the new tunnel in the first 24 hours of opening.

Despite fears of increased traffic and drivers unfamiliar with the new layout of the $1.4 billion roading project, the Monday morning peak hour passed by without incident and minus the anticipated big queues.

The NZ Transport Agency today said by midnight 78,000 vehicles had travelled through both tunnels since it opened to traffic early Sunday morning.

Heavy traffic was expected through the twin 2.4km tunnels during the peak Monday morning period, however the traffic was free flowing.

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"It's been a great Monday morning across the Auckland motorway network. Traffic has been free-flowing through the tunnel as well as on State Highway 16 and State Highway 20," said agency spokesman Brett Gliddon.

The transport agency earlier thanked motorists for a smooth start to the working week, tweeting traffic had flowed easily in both directions.

Gliddon said the Waterview Connection had already improved journey times on SH1 between Papakura and the city.

"The Waterview Connection isn't designed to remove peak time congestion altogether but so far it has provided a better balance of traffic flows across the road network," he said.

He said about 4000 vehicles an hour were travelling in both directions when traffic peaked at lunchtime yesterday with an extra 2200 vehicles on the motorway system than on a typical Sunday.

Motorists this morning praised the new motorway connection on the NZTA's Facebook page for dream runs into work. Some said the new tunnel slashed travel times in half.

"Thanks NZTA was a good experience this morning to drive through the tunnel. Normally it takes 40 mins from Massey Rd to Lincoln Rd but this morning it only took me 18 mins to get at my work," posted Roneel Krishna, who helped deliver concrete to build the tunnel.

"Went through it this morning heading north, good as gold!" posted Paul Belli.

Others said the project had also made a noticeable impact on surrounding roads.

"Yay! Local roads in area much quieter today- hope that continues," posted Clare Brown.

Earlier this morning the NZTA warned motorists using the tunnel link to get to work to be prepared for heavy traffic.

However despite fears traffic flowed freely in both directions from 6am with no problems despite wet roads.

Conservation Minister Maggie Barry this morning tweeted from inside the tunnel saying using the new motorway link saved 10 minutes on her commute to the airport.

Yesterday Gliddon told motorists to be patient and allow plenty of time as many motorists navigated the reconfigured motorway system for the first time.