The RAIB have released their latest Safety Digest which is related to the slow speed derailment of Nottingham Express Citadis 219 at Highbury Vale on 30th September 2022. This is not a full report as it has been decided a full investigation is not needed as the causes of the incident are similar to other cases on the main line railway; the Safety Digest enables the RAIB to release learnings to the parties involved as quickly as possible.
This derailment happened at 0717 on 30th September 2022 when Citadis 219 was travelling towards Phoenix Park. As many of you reading this will be aware at the lines to Phoenix Park and Hucknall split at Highbury Vale and the derailment happened at the set of points (HVP3) which govern moves between the two lines.
Before the accident these points had been reported as defective and a team of technicians had been sent to the scene at the start of their duty on that morning to investigate the cause of the fault. All tram drivers had been informed by radio about this so they were aware of the issue and that there were technicians on site.
On arrival at the preceding stop of David Lane, the driver of 219 noticed that the points indicator was showing that HVP3 were in an intermediate position. They then used in-cab controls (as per normal practice) to command the points to move onto the correct route to Phoenix Park and before they departed the stop the indicator showed that this had happened and it was in the correct position when the tram moved forward.
Less than a minute after 219 had departed David Lane, 236 arrived with a service bound for Hucknall. The driver of 236 had planned to leave enough time for 219 to clear the points but due to fog they were unable to see 219 and so called the points for the straight line to Hucknall, just as 219 was starting its move over the points. This caused the points to move and the front wheelset of 219 encountered them in the intermediate position leading to the slow speed derailment (the driver of 219 was only going at 7mph instead of the line speed of 16mph as they were aware that maintenance work was taking place).
The RAIB confirmed that the cause was down to the changing of the points as 236 had called them whilst 219 was travelling over them, although this was not down to error by either driver. In normal operation there is a detector in the track circuit which would prevent the points being changed until after the tram has passed through the area.
In this instance though because of the work taking place – which had seen the technicians resetting the controller to clear an error – the set route for the points had been cleared from the system and when 236 called the points it was able to do so as the system didn’t realise there was another tram on the points.
In summary the RAIB have said that the incident demonstrates the importance of:
- Recognising that working on assets in degraded conditions can mean that normal technical and operational risk controls may no longer be present
- Taking the time to understand the risk that reactive work, such as responding to faults, may bring the staff on site, to safety-critical systems and to vehicles using the infrastructure
- Staff dealing with safety-critical equipment working within their competencies and taking appropriate action when they recognise that they are not
Fortunately, there were no passengers on board 219 and the driver was unharmed in the derailment. There were damage to the tram and also the infrastructure.