Works have started on one of the worst accident black spots on State Highway One.
The work, which started on Sunday, involves contractors felling trees and removing vegetation in the Dome Valley, north of Auckland.
New Zealand Transport Agency (NZTA) said crews would be working overnight from 7pm to 6am, to minimise traffic disruption.
The job will take about two weeks.
The work will clear the way for major safety improvements along a 15km stretch from Wellsford to north of Warkworth, and includes widening, right-hand turning bays and flexible road safety barriers.
The winding road through the Dome Valley is notorious for crashes.
NZTA is advising motorists travelling between Northland and Auckland to plan ahead and allow extra time for their journeys.