A mechanical failure sent a logging truck's trailer skidding into a ditch, disrupting traffic on the morning commute between Dargaville and Whangarei.
The accident happened on State Highway 14 near the intersection with Tatton Rd at about 6.55am yesterday.
Senior Constable John van Pomeren said the truck was heading east when the brakes for the trailer locked and caused it to skid around and go off the road and into a ditch.
Mr Van Pomeren said for some reason the jackshaft between the two rear axles on the truck came away. He said it "flew" out, and chopped a couple of air lines which caused the trailer's brakes to lock on.