Tram speed risks studied after Sheffield incident
The Rail Accident Investigation branch has issued a Safety Digest following an incident on the Sheffield Supertram network in July where a tram approached a sharp bend too fast.
At 1558 on July 19, a Sheffield Supertram tram entered a tight curve on the approach to Middlewood tram terminus at 23mph. The maximum speed at this location is 10mph.
The driver realised he was going too fast just before the tram reached the curve and applied the emergency brake to stop the tram.
One passenger was injured when she was thrown from her feet by “excessive” lateral accelerations and hit the tram’s exterior doors.
The impact caused a component in the door system to fail and the door to partially open. The RAIB notes that although the passenger remained in the tram, she could have been ejected through the open door. At least one other passenger suffered a minor injury.
The investigation concluded that the driver lost awareness of where the tram was in relation to the curve and did not slow down to the 10mph speed limit.
A sign reminding drivers of the reduced speed limit was provided at the start of the curve, but there were no advance markers relating to the reduction in permissible speed preceding this.
Since the incident, Stagecoach Supertram has installed a ‘step down’ speed restriction of 20mph 100m before the start of the curve at Middlewood. It has also identified another on-street curve with similar characteristics and introduced a speed restriction there.
The accidental door opening was caused by the failure of a connection between a ball joint and vertical shaft. This failure disconnected the door’s vertical rotating shaft and corresponding door leaf from the locking mechanism which allowed the door to open.
In its Safety Digest, RAIB says the incident demonstrates the importance of drivers taking special care when approaching high-risk locations, particularly where a substantial reduction in speed is necessary. It also says it is important that tram owners and operators assess operation risks in such locations and ensure that mitigations are in place.