Fatal smash leaves behind no clues

Police have no clues why the man at the wheel of a Toyota Cynos crossed the highway centre line at Mangatawhiri and slammed head-on into a 40 tonne truck.

The car's driver, North Shore resident Jean Morvan, 24, was killed instantly.

Constable Neil Holyoake of the Counties Manukau Serious Crash Unit said the truck was heading west and the car was eastbound on State Highway 2 when they collided under the Koheroa Rd overbridge just after 10pm on Monday.

Mr Holyoake said the impact was entirely within the westbound lane, the Toyota having crossed the centre line.

"It was a huge impact," he said. "The driver had no chance of surviving."

What remained of the Toyota had to be removed to a yard where Mr Morvan's body could be extracted.

Road conditions at the time were good and the weather was clear. Visibility on the straight stretch of road would have been good, despite there being no streetlights on that section of 100kmh highway.

"We'll interview the last people to see the truck driver. We'll get as much technology as we can - phone records, GPS from the truck, and anything else we can get and we'll see if we can determine why he's crossed the centre line."

Mr Holyoake did not suspect alcohol to be a factor but blood analyses would provide a definitive answer.

If anybody saw the truck or the car shortly before or at the time of the crash, he would appreciate them coming forward.