Police described it as "terrifying''.
Glasgow Bin Lorry Latest
An inquiry into a bin lorry crash that killed six people has heard evidence from an expert who examined the truck.
Phil Balderstone, from the Transport Research Laboratory (TRL), examined the Glasgow council truck to see if anything could have been done to halt it when the driver apparently fell unconscious.
Six people were killed in the tragedy on the city's Queen Street three days before Christmas and a further 10 were injured.
Expert witness Mr Balderstone, 46, said he was able to pull the handbrake lever from a standing position on the crew bench behind the driver's seat.
A photograph of him stretching over a yellow safety bar towards the controls was shown on the third day of evidence in the fatal accident inquiry at Glasgow Sheriff Court.
Mr Balderstone said he was able to apply the handbrake lever "comfortably'' while standing on the bench without a seat belt on, but he acknowledged being able to do so would depend on a person's size and mobility.
He said that from a seated and belted position he could only just reach the top of the handbrake lever, but he was able to pull it down using his foot.
The expert agreed with Solicitor General Lesley Thomson, leading the inquiry, that some training would be required to know how to operate the vehicle controls.
He said pulling the handbrake in an emergency could cause the occupants of the vehicle to be thrown forward and risked a collision to the rear as it did not trigger a brake light.
Ms Thomson said: "If this is the only option left, there's nothing else you can do, is it an option you should take?''
Mr Balderstone agreed that it was.
Binmen Matthew Telford, 46, and Henry Toal, 47, were belted behind driver Harry Clarke when the truck lost control and veered on to the pavement outside the Gallery of Modern Art on December 22.
Erin McQuade, 18, and her grandparents Jack Sweeney, 68, and Lorraine Sweeney, 69, from Dumbarton, West Dunbartonshire, were struck and killed by the lorry.
Stephenie Tait, 29, and Jacqueline Morton, 51, both from Glasgow, and Gillian Ewing, 52, from Edinburgh, also died.
Mr Telford told the inquiry earlier that he punched and shouted at Mr Clarke to try to rouse him and that his slumped body prevented him from accessing the controls.
Mr Toal said it did not occur to him to try to pull the handbrake.
The men, who do not drive, escaped with minor injuries when the truck careered along the packed street and crashed into the side of the Millennium Hotel in George Square.
Mr Balderstone said emergency breaking systems used on trains and trams were not suitable for road transport.
Other technology can assist in situations where the driver is incapacitated, the expert said, but he could not be certain they would have avoided the events of December 22.
These include autonomous emergency breaking (AEB), driver facial recognition and pedestrian detection systems, which the truck did not feature.
Ms Thomson said: "Are you able to provide any views as to which, if any, of the safety technology could have avoided this (pedestrians being struck)?''
Mr Balderstone said the current specification of AEB systems fitted to large goods vehicles has no capacity to detect pedestrians and "sadly it would not have made a difference''.
He said that new technology currently being looked at, and already available in some industries, could potentially have a mitigating effect in this type of accident.
He concluded in his report: "In summary, the risk of injury in collisions due to driver incapacitation can currently be reduced with the fitment of modern technology.
"The technology is becoming more common within the market, but is far from being widespread or a mandatory fitment.''
The inquiry continues on Monday.
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