tonnes of soil had been removed. Investigations The BTP, ORR and Rail Accident Investigation Branch (RAIB) opened investigations into the accident. The BTP ruled out criminal activity as a cause of the derailment. On 21 September 2020, the RAIB released an update about their investigation. It had been found that at some point on the journey, the brakes on the third wagon had become applied. The leading axle of the front bogie had seized, causing a flat spot to develop on one of the wheels, along with a false flange. As the train traversed a set of points, the wheel distorted the track under the train, causing the derailment. The wagon had run for more than in this condition. The brakes had become applied due to a fault with the mounting of a relay valve on the wagon. On 30 October 2017, the brakes on a wagon of a tanker train from Robeston had seized causing a severe flat spot, before the axle became free again. Track between Carmarthen Junction and the Llangyfelach Tunnel, a distance of , was severely damaged. On 5 November, the RAIB released an Urgent Safety Advice notice relating to the maintenance of wagons used primarily for the carriage of dangerous goods. On 6 March 2021, an oil train caused severe damage to track between Pencoed and Llanharan following the development of wheel flats on a tank wagon, caused by the brake system falling apart whilst the train was on its journey from Robeston to Theale. The RAIB, in its notification of an investigation, drew attention to similarities with the 2017 incident and the derailment at Llangennech. The RAIB published its final report on 13 January 2022. Nine recommendations were made. References Notes Railway accidents in 2020 2020 in Wales Derailments in Wales 2020 fires in the United Kingdom Train and rapid transit fires August 2020 events in the United Kingdom History of Llanelli Oil spills in the United Kingdom Environment of Carmarthenshire 2020 in the environment