Police are appealing for dashcam footage after detaining crash survivors in the Royal Hobart Hospital for questioning.
A red Commodore ute lost control on a bend on Huon Road at Fern Tree early yesterday, hitting trees.
A 19-year-old Sandford woman was thrown through the windscreen and was taken to hospital in a serious condition.
The driver, an 18-year-old Grove man, and a male passenger avoided life-threatening injuries.
Police have ruled out road or weather conditions as factors.