The Rail Accident Investigation Branch has issued a report into an incident in November 2021 when an empty passenger train collided with part of a fallen tree between Wrexham General and Chester.

The incident happened at about 2313 on Friday, 26th November 2021 on the down Wrexham line. A Transport for Wales Class 150 diesel multiple unit travelling at 46 mph (74 km/h) between Wrexham General and Chester ran into a fallen tree in a cutting about 68 metres beyond the exit of Balderton tunnel. The leading axle of the train was derailed, but there were no injuries, although there was minor damage to the train and to lineside signalling equipment.

The fallen tree was about 50cm in diameter and had been growing just beyond the crest of the cutting, about 50cm outside the railway boundary fence about 9 metres from the railway line.

Before this collision occurred, after leaving Wrexham, the same train had already collided with two other trees obstructing the railway. They all happened whilst high winds from storm Arwen were affecting much of the UK, including the Wrexham area.

Upon inspection, Network Rail staff found that the tree which caused the derailment was in ‘apparent good health’ before it fell, and that the cause of the tree falling was ‘extremely high wind speeds’ coming from an unusual direction.

Between 22.00 and 23.00, a Meteorological Office weather station about 2.5 miles north-west of the accident site recorded north-north-westerly wind with an average speed of 36 mph and gusts up to 64 mph. In the following hour, during which the accident occurred,, wind speeds increased to 39 mph with gusts up to 69 mph, and were indicative of the conditions likely to have been prevalent at the scene of the derailment.

The train left Wrexham General station at 22.12, and at 22.17 struck two trees close together at a speed of 38 mph. The driver called the signaller to report the incident, inspected the train and finding only superficial damage removed those portions of the trees still obstructing the railway line. At 22.29 the driver informed the signaller that the train was able to proceed and resumed the journey. About a minute later it struck a third tree while travelling at 18 mph and at 22.34 the driver called the signaller to report this collision. He then reversed the train to clear the obstruction, removed portions of the tree and inspected the train.

At 22.54 the driver called the signaller again, and having cleared the tree from the line and checked the train, agreed that the train should continue to proceed at caution until the bottom of Gresford bank. At 23.09  the train driver informed the signaller that he had reached the bottom of Gresford bank without incident, and at 46 mph which was less than the permitted line speed of 60 mph, struck the tree shortly after exiting Balderton tunnel, causing the leading axle of the train to derail.

If a train driver reports a collision with an obstruction, signallers must contact route control, and not to allow the driver to proceed until approved to do so by control. On this occasion, the signaller did not contact route control until after the second collision, and route control staff did not then instruct the signaller to restrict the movement of the train in any way.

Before the derailment of this train, Storm Arwen had caused serious disruption to Network Rail infrastructure. By this time, 19 incidents involving fallen trees had been reported, including nine within the North West route.

Network Rail procedures for managing operational risk from extreme weather requires routes to produce planned responses for actual or forecast breaches of specified weather-related thresholds such as high winds, heavy rain or low temperatures. There are thresholds for ‘extreme’ and, less onerous, ‘adverse’ conditions, and Network Rail describes extreme weather as ‘so severe that consideration has to be given as to the level of service which can be safely operated’. Adverse weather is that ‘known to be challenging to reliable operations’.

If an ‘extreme’ weather threshold, or multiple ‘adverse’ weather thresholds, are forecast to be exceeded, the relevant route control staff are required to convene an extreme weather action teleconference (EWAT). This is intended to co-ordinate weather-related responses from various parts of the rail industry and to provide a forum for ‘structured expert judgement’ where this is needed to support decision-making. In addition to convening an EWAT before an extreme weather event, route control staff are required to conduct an EWAT during an extreme weather event if appropriate.

On the day of the incident the expected wind speeds within the North West route escalated from ‘adverse’ to ‘extreme’ on the morning of the accident. Although an EWAT was required to be convened in these circumstances, North West route control staff did not convene one because they believed that an EWAT held the previous day had sufficiently considered the weather-related risks. Instead, both forecast and observed weather conditions were monitored hourly.

Network Rail states that wind speeds were shown not to have breached thresholds in those areas where the maximum permitted line speeds were greater than the emergency speed restrictions that would have been required by its procedures.

It is unlikely that holding an EWAT would have prevented this accident because it was probable that a 50 mph speed restriction would have been put in place, and the train was travelling at under this speed when the accident occurred.

Also, the topics to be considered during an EWAT do not take into account wind direction, neither do the wind thresholds. The consequence is that there may be more than the expected tree falls due to the unusual direction of the wind, which may not have been realised by those forming the EWAT, even had one been convened.