The Rail Accident Investigation Branch (RAIB) have released an initial report into the causes of the recent fatal tram accident in Croydon on 9 November 2016. The accident, which cost the lives of seven people and seriously injured another 51, is one of the most serious rail accidents in London since the Moorgate accident in 1975.
Initial reports and the RAIB
For those unfamiliar with the way the RAIB works, it is worth noting that their reports are not intended to allocate blame or liability. They are created to establish the cause of an accident and recommend any safety measures that can be implemented to prevent a similar accident from happening again. As a result RAIB reports are always very thorough and take considerable time to pull together. In some cases, however, the seriousness of the accident warrants an initial report aimed at highlighting any obvious safety issues which can then be corrected straight away.
This initial report for Croydon should thus not be taken as a complete or definitive account what happened that day. It does, however, provide a basic timeline of events.
The tram before the accident
Tram 2551 departed New Addington at approximately 05:55 that morning. The weather was dark and rainy. The driver was the only member of staff aboard and by the time the accident happened it was carrying roughly 60 people. The tram itself was one of the original Bombardier units built for the Croydon tram fleet and had been in service since 1998. It was equipped with forward-facing and internal CCTV, but the RAIB’s initial findings are that this CCTV was not working at the time of the accident.
Importantly for the purposes of the investigation, the tram was also equipped with an On Tram Data Recorder (OTDR). This is what various media outlets have been referring to as the tram’s ‘black box’ and whilst it is not as fully-featured as the kind of black box systems used on aircraft, it does record some critical information about the speed the tram was travelling at and how it was being controlled.
The tram stopped, as planned, at five stops before reaching Lloyd Park. After this, it began to accelerate as it headed towards the next stop at Sandilands.
The Sandilands junction curve
Between Lloyd Park and Sandilands, Tramlink runs on its own dedicated track corridor. This includes about 900m of open ground, which gives way to the Sandilands tunnels – three tunnels in very short succession (about 500m in combined length). Beyond the last tunnel is a short cutting (about 100m long) at the end of which, just before Sandilands junction, is a left-hand curve about 30m in radius.
There is thus about 1500m of relatively straight running, with a slightly falling gradient, leading up to the curve. For much of the distance between Lloyd Park and the curve the speed limit on the line is 80km/h, but this drops to 20km/h shortly in advance of the curve itself. A reflective sign warning about the drop in the speed limit is located about 30m ahead of where the tram derailed.
The tram’s approach to the curve
According to the data on the OTDR, tram 2551 accelerated up to a speed of 80km/h after it left Lloyd Park. In order to reduce its speed to the 20km/h by the time it reached the reflective speed limit sign, it would have to brake at its full service rate 180m in advance of it. This the tram didn’t do. Some braking was applied within that distance, but it was only enough to reduce the Tram’s speed to about 70km/h by the time it reached the sign and the curve beyond.
The tram, still travelling at about 70km/h, left the track when it encountered the curve. It turned over onto its right-hand side and continued forward for about 25m before coming to a stop. The RAIB have not found any evidence so far of either track damage or obstructions on it which might have contributed to the accident.
Initial recommendations and next steps
The RAIB have recommended that further steps be taken to reduce the risk of excessive speed in the lead-up to Sandilands junction curve before the line is reopened. They have suggested an additional speed restriction on the approach, more signage warning of the upcoming existing speed restriction, or a combination of both.
The in-depth investigation into the accident’s causes continues, and we’ll cover it in full here when it is eventually completed. In the meantime, the RAIB have requested that any witnesses to the accident contact them.
You can read the entire initial report here.
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