Horror highway crash driver 'starting to wake up'

The man behind the wheel of a Toyota Landcruiser, filmed driving erratically before crashing head-on to another vehicle, is "starting to wake up".

Shaun Southern remains in intensive care two days after the deadly crash that claimed the life of mother-of-two Jenni Pratt and caused serious injuries to her 54-year-old passenger Karen Williams.

Homicide detectives are standing by to formally interview the 45-year-old Southern over the horrific crash on the Bussell Highway in Capel on Saturday afternoon.

Crash driver Shaun Southern. Picture: 7 News
The horrific fatal crash scene. Picture: 7 News

According to 7 News, detectives are investigating whether Southern can be charged with murder or manslaughter as he starts to wake up.

Major Crime Squad detectives are still trying to piece together what led the Bunbury man to Saturday afternoon's deadly rampage.

Ms Pratt was just minutes from home when she was hit head-on by Southern, who was driving on the wrong side of the road.

Passersby raced to her aid but sadly Ms Pratt died at the scene.

Mother Jenni Pratt. Picture: 7 News
Southern's Landcruiser rolled and caught fire. Picture: 7 News

"Mum's brightness, beautiful smile and the way she listened and cared, meant that so many people lived and relied on her as a companion, someone to confide in and a true friend," Ms Pratt's family said in a statement.

Doctors at Bunbury Hospital say Ms Williams' condition has improved and she's now in a stable condition.

Highway horror: Driver filmed leading up to fatal crash

Passersby rushed to Ms Pratt and Ms Williams' aid. Picture: 7 News
Southern was filmed driving erratically in the lead up to the crash. Picture: 7 News

Police are still appealing for witnesses who may have seen Southern's Landcruiser on Wonnerup Beach, or driving on Layman Road or the Bussell Highway.

Anyone with information on the crash should call Crime Stoppers on 1800 333 000.