An hour in agony, as pedestrian pinned by runaway truck trailer

A pedestrian is lucky to be alive after a 16-tonne trailer came loose from a truck in the Adelaide suburb of Glynde this morning, careening down the road and crushing him on the footpath.

Onlookers described how the man was pinned, seemingly in agony, for almost an hour. They watched in horror, unable to help.

Local worker Gillian Bowie said: "His legs were trapped underneath and he was just screaming so he was still conscious".

"I think they tried to find a hydraulic jack to try and get it off him but too heavy," she said.

A medical retrieval team joined paramedics and fire fighters during the delicate rescue mission.

The 48-year-old was rushed to the Royal Adelaide Hospital with serious injuries.

The subsequent investigation showed a trail of brake fluid stretch 50m along Payneham Rd and Glynde, showing just how far the trailer skidded along the road before it mounted the curb and struck the man.

Exactly how the trailer broke loose is still unknown.

Police closed city-bound lanes as they scoured the vehicle and the road, eventually locating parts from the truck's connection with the trailer.

The nightmare accident comes less than a fortnight after two people were killed by an out of control truck at the bottom of the South Eastern Freeway, fuelling concerns about the safety of heavy vehicles on our roads.