Transport Minister Steven Joyce says the opening of the Victoria Park tunnel to traffic will resolve the last major bottleneck in central Auckland.
The $340 million tunnel, along State Highway One is now open to two lanes of traffic.
A third lane will open to northbound traffic in March next year.
Mr Joyce says more than 150,000 vehicles use the route each day and the tunnel will reduce traffic congestion.
He says it could eventually cut journey times by up to 20 minutes.