The Rail Accident Investigation Branch (RAIB) have finally released their full report into the collapse of the overhead line near Jewellery Quarter on the Midland Metro system back on 20th April 2011. This was a major incident for the tramway with severe damage occurring to the overhead which required the service to be suspended completely until 24th April after which a limited service was operated until 28th April when normal services were
resumed. The outcomes of the investigation have not been able to fully determine quite why the overhead came to collapse although a number of possible theories have been ascertained and as is usual with these investigations a number of recommendations have been made to ensure occurrences like these can be avoided in the future.
The incident happened at 1325 on 20th April 2011 when tram 13 travelling towards the Jewellery Quarter tramstop struck an item of overhead line equipment (OLE) which had already become partially detached from its supporting pole. This caused damage to the tram and also led to a progressive collapse of a significant stretch of overhead line which in turn saw more damage sustained by the tram as it continued to strike further OLE components. The tram suffered damage to the front and rear windscreens, the side windows of the driver’s cab, the saloon windows, the doors and severe damage to the pantograph with a number of passengers suffering minor injuries as a result of flying glass (three adults and three children required hospital treatment). The driver bought to the tram a stand at Jewellery Quarter tramstop to allow the passengers to alight, as normal, onto the platform.
As a result of their investigations the RAIB concluded that the reason that the cantilever on the OLE became detached was because part of the assembly which connected to its
supporting pole had fractured as it was mechanically overloaded. Unfortunately they were unable to figure out why this had happened but did identify two possible explanations. Firstly that the cantilever became jammed and unable to move freely and this allowed the forces present in the equipment during normal operations to act in a way that overloaded the reducing sleeve.
The other possible explanation – and one which is considered by the RAIB to be more likely – was that a tensioned rope forming part of the OLE became damaged after coming into contact with other OLE components. The subsequent parting of this damaged rope
may have both momentarily restricted the movement of the cantilever and also introduced abnormally high loads into the system which would have overloaded the reducing sleeve.
The report also suggested that there may have been the incorrect installation of the OLE as the contractors involved in this work had inadequate information and were also, possibly, under time pressure and the potential impact of design modifications on the performance of the overhead line had not been appreciated. Concerns were also expressed over the incident management of the tram crew following the incident and if the training of staff to handle similar emergencies was sufficiently comprehensive.
As a result of the incident, several recommendations have been made to National Express Midland Metro in relation to the following areas:
- Measures to prevent damage to components resulting from unintended contact between them
- Access to up-to-date and relevant technical information
- The need for an understanding of relevant failure mechanisms within the OLE system
- The change control of critical OLE components
- The management of the possible risks created by a driver becoming incapacitated during an incident
- The maintenance of mandatory competences held by members of tram crew
* The full RAIB report into the incident can be downloaded at http://www.raib.gov.uk/cms_resources/120927_R212012_Jewellery_Quarter.pdf