State Highway 1 has reopend near Levin a crash this morning involving a truck and trailer.
Police suggest motorists still consider delaying their travel, given there
may be delays in the area.
The road was closed earlier this morning after the crash and rail services were also suspended as the truck was left precariously near the tracks.
By the time one lane was opened later in the morning, traffic had backed up more than 4km in both directions, almost to Levin in the north and to Otaki in the south.
Police closed the road about 11.15am for heavy lifting equipment which was brought in to right the truck.
The road was closed for about three hours.
Police and fire crews were called to the scene at the Manakau overbridge near Levin just before 8am.
Senior Sergeant Sarn Paroli said the southbound truck and the northbound car had collided head-on on the south side of the rail bridge.
"The driver of the car, a man in his 30s, was airlifted to Palmerston North Hospital with serious injuries."
Paroli said the truck driver was uninjured but shaken.
KiwiRail inspector Eddie Dargaville said the track would also be closed until further notice.
A resident, who lives near the accident scene and declined to be named, said the site was notorious for accidents.
"In the 50 years I've lived here, I would have seen hundreds of accidents," the woman said.
She said the speed limit should be lowered on the stretch of road between the rail overbridge and the Waikawa Stream bridge.
Further up the country, a crash was causing traffic headaches for motorists on the Northern Motorway.
The collision was blocking the right-hand lane of the Onewa on-ramp.