Teen boy fights for life after crash that kills WA mum

A 17-year-old boy is still fighting for life a day after a crash that killed a mother and injured two others south west of Perth.

Trudy Clarke, from Waroona, was killed when the grey Holden Commodore she was a passenger in collided with an oncoming truck on South Western Highway yesterday afternoon.

Liam Ewan Passmore was trapped inside the wreckage and remains in a coma in Royal Perth Hospital's intensive care unit.

The 17-year-old's family are holding vigil by his bedside and have urged others to "hold on to their loved ones tightly".

"You never know when this sort of tragedy could strike," the family said in a statement to 9News.

Kyenan James Nielsen, 18, and driver Mark Tomlinson, 43, was also seriously injured in the crash and are being treated in the state trauma unit.

The crash highlights WA road toll figures that show a disproportionate number of fatalities on country roads, with 85 already this year compared to 50 deaths on metropolitan roads.

The Road Safety Commission claim three quarters of all deaths on country roads are due to driver inattention.