West Oxfordshire councillor Colin Dingwall witnessed the moments before the crash and told the Oxford Mail: "I've seen a lot of things in my 50 years on the road, but never a caravan coming the wrong way up the M40.
"Luckily I and the cars near me managed to pull into the middle lane and get out of the way.
"He must have been going about 60mph [95km/h]. It was a car with foreign plates pulling a caravan. It didn't look to be slowing down.
"I had about two seconds to react."
Senior investigating officer Sergeant Beth Walton, from the Serious Collision Investigation Unit of Thames Valley Police, said: "We are in the early stages of the investigation, in which sadly three people died, and our thoughts are with their families."
A number of people who witnessed the Forester being driven in the wrong direction described what happened on Twitter.
Liz Hindmarsh posted: "My husband had to swerve into the middle lane otherwise he'd have been hit."
Oliver Hayes wrote: "We also had to swerve, seemed at least 70mph driving head on in our lane at junction 8... did not look accidental.
"Called the police who said they'd had multiple calls by that time. Scary stuff hope no fatalities but looked inevitable the way they were driving."
