The speed limit on State Highway One across the Brynderwyn hills, south of Whangarei, has been permanently lowered.
The Transport Agency says it is a notorious black spot. Eight people have died in crashes on the Brynderwyns in the past five years.
The speed limit is now 80km/h, instead of 100km/h, from 27 May.
The lower speed is in force for almost 6km between Waipu Gorge road on the northern side of the hills to the Piroa Stream Bridge on the southern side.
The agency says it does not believe the change will add any significant time to people's journeys.