BARRIE, ONT. -- A 60-year-old woman died following a single-vehicle collision on Highway 400 near Port Severn.

Southern Georgian Bay OPP said the North York woman's car hit a centre rock median while travelling north of Muskoka Road 34 (White's Falls Road) shortly before 2 p.m. on Tuesday.

The northbound lane was closed for several hours following the collision. It was reopened shortly after the dinnerhour.

Investigators are left trying to figure out what caused her to collide with the rockface.