A truck that narrowly escaped disaster in South Australia has been fined as a result, with investigators noticing the rig had a modified speed limiter.

A truck was reportedly rolling on the South Eastern Freeway near the town of Crafers when it failed to stop at an intersection. This was likely due to faults with its brakes and steering wheel.

The driver may or may not have been aware, but either way his quick thinking led to a disaster averted. He was forced to swing into an emergency arrester bed to bring the B-double to a halt.

The incident was investigated by the South Australian Department of Planning, Transport and Infrastructure, with auditors discovering the brakes, steering and speed limiter had been tampered with or were defective. The A-trailer had defective brakes too.

Authorities have declined to name the company involved in what could easily have been a much worse incident, though a fine has been issued along with a warning to all drivers that tampering with safety features rarely ends well.