A site supervisor and a controller of site safety saw the trolley approaching on the downhill gradient at around 20mph (32 km/h) and shouted a warning, providing enough time for staff to get clear of the track.
No one was hurt in the accident, but the trolley was damaged after it collided with a piece of equipment, which was also damaged.
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A report by the Rail Accident Investigation Branch (RAIB) found that the incident, which happened on 26 May 2024, was caused by the operator intentionally defeating the failsafe function of the trolley’s braking system.
A failsafe brake automatically stops movement when power is lost or when a safety condition is triggered, preventing uncontrolled movement or damage.
The design of the trolley made it possible for the failsafe to be deactivated, which the operator was also aware of.
The rail accident watchdog said the ergonomics of the trolley brake system made it tiring to use, potentially encouraging the operator to defeat the brakes.
The operator was unaware that there was a risk of the trolley running away at this location.
Underlying factors
RAIB identified two underlying factors leading to the accident: the product acceptance process employed by Network Rail did not manage the risks incurred by this design of trolley; and a lack of clarity in site leadership roles meant risks were not being effectively managed.
A further probable underlying factor was that the defeating of the braking system on this type of trolley is a known issue, but no effective action had been taken to eliminate the practice.
As a result of its investigation, RAIB has identified two “learning points”. These are the importance of staff not rendering the braking system ineffective when working with trolleys of this type; and the importance of controllers of site safety accompanying work groups to personally observe and advise them.
