There are four speed cameras in Auckland's newly-opened Waterview tunnel - and police say they hope no one will be caught going too fast by any of them.
Advance warning has been given to drivers on NZ Transport Agency signage saying the cameras will be enforcing from this afternoon.
The speed limit in the tunnel is 80km/h.
Road Policing Manager of Operations, Inspector Pete McKennie, said the move to enforcement mode follows a period of rigorous testing, which has involved operating the cameras to monitor traffic flows, with Police and the Transport Agency using alternate methods of enforcement and education to encourage safe driver behaviour.
There was "no excuse" for drivers to miss the warnings, he said.