New figures have revealed Auckland's Waterview Tunnel has helped shave nearly 20 minutes off some commuters' journeys.
The $1.4 billion tunnel, which is New Zealand's most expensive road, opened in July.
Transport Agency figures show more than 6.5 million vehicles have travelled through the tunnels since then, with more than 400,000 trips each week.
In a statement, the NZTA said travelling from the airport to the CBD during peak afternoon times used to take between 35 and 44 minutes via Manukau Road and Gillies Ave, but it now takes 25 minutes through the tunnel.
The tunnel has also slightly improved travel times on State Highway 1 between Papakura and the city - the trip used to take between 46 and 70 minutes but now consistently takes an average of 49 minutes.
NZTA system design manager Brett Gliddon said the road meant traffic was now spread more evenly across the city's motorways.
"Waterview has been a game changer but we're also continuing to work on Auckland's other key corridors and building a new transport system to cater for the city's population growth."
He said the Waterview Tunnel was not designed to remove congestion, but was a big step towards completing Auckland's transport system so people had more options and certainty about how they get around.