A truck, seven cars and a bus collided at Glen Osmond Road and Portrush Road, near the bottom of the freeway, at 3.45pm on Sunday.
Witnesses reported seeing smoke coming from the Mitsubishi truck, which was towing a trailer, as it swerved in and out of traffic towards the intersection.
Police said the truck was unable to stop as it entered the intersection before crashing into a Hyundai SUV and a bus, both of which were stationary at the time.
The truck then continued to plough across the intersection, taking out another five vehicles.
The impact caused two more cars to crash.
The Mitsubishi truck driver, a 60-year-old man from Queensland, was taken to hospital with non-life threatening injuries.
The bus driver was the first to alert emergency services.
“There’s a truck just come down the hill at the Portrush Road intersection and whacked millions … lots of cars, we need police, ambulances and everything here right now,” he said in his call for help.
Witness Kaleb James said “it was a God awful noise of screeching and clashing and when we got here all the trucks had started to arrive”.
SA Police said major crash unit officers were investigating.
“Nine people from the scene have been transported to various hospitals within Adelaide with non-life threatening injuries,” police said in a statement.
Steve Shearer from the South Australian Road Transport Association told 9News while the freeway is mostly safe, a third arrestor bed could save lives.
“We’ve got to try with the third arrestor bed and accept that it won’t be 100 per cent perfect but if it saves just one or two lives, it is worth it,” he said.
Premier Peter Malinauskas told 9News this morning his government will consider the options once the investigation into yesterday’s crash is complete.
It’s the latest serious incident on that section of the freeway.
A safety overhaul was sparked by two deaths when a truck lost control in August 2014.
A person also died that January, while in October 2010 a pedestrian was hit and killed by a runaway truck.