The Automobile Association (AA) is warning the Waterview Connection's honeymoon period ends today.
Auckland's traffic is expected to return to its sluggish self on Monday, with schools and universities back from holidays.
AA spokesperson Barney Irvine says Monday morning will be the tunnel's biggest test.
"We still expect to see better traffic flow than we saw before the tunnel, but the gains won't be as pronounced as they've been for the last couple of weeks."
Mr Irvine says the solution for Auckland's traffic woes is more public transport, better roads and greater use of technology.
"It's going to take new roading projects, particularly around the new growth areas. It's going to take more public transport, it's going to take more use of technology, and it's also going to take some changes in behaviour."
Speed cameras have recently been turned on in the tunnels to ping people going more than 80km/h.
"So far it's passed the test with flying colours," says Mr Irvine, "but this is going to be the big moment. All schools are back universities are back."