Driver may have had coronary at wheel
The bin lorry that left six people dead and up to 10 more in hospital was seen veering out of control through Glasgow city centre.
The vehicle is believed to have struck the first pedestrian outside the Gallery of Modern Art, before careering down Queen Street and through traffic light road junctions before coming to a stop after hitting the Millennium Hotel in George Square.
Investigations into the incident are still in the very early stages, but one element experts will examine is how the vehicle travelled around 300m in an almost straight line before it came to rest.
Eyewitnesses reported seeing the driver of the Glasgow City Council refuse vehicle slumped over at the wheel, prompting speculation that he may have suffered a heart attack or other physical seizure.
He is now being treated in hospital.
A spokesman for the Institute of Traffic Accident Investigators said that vehicles, even large ones, can carry on for a considerable distance if there is an "unintended acceleration", which could be caused by a driver falling ill - and perhaps going into a spasm - with their foot on the accelerator, or by someone inadvertently pressing the accelerator rather than the brake.
He said: "Without speculating on this incident, there might be a number of causes for a vehicle to travel a considerable distance like this.
"If there is no external influence on the steering direction of the vehicle, then it will continue in a straight line.
"An external influence might be a driver applying steering, or the wheels coming into contact with something like a kerb.
"Regarding the distance travelled, one would expect a vehicle to slow if the driver's foot had been removed from the accelerator, due to engine braking."
The spokesman said that in the eventuality of a brake failure a driver can also slow a vehicle by changing down through the gears.