On 12 September 2006 a South West Trains service from Waterloo to Effingham Junction derailed as it approached Epsom station. One bogie of the fourth carriage derailed while the train was travelling at 17mph. The train came to a stop partly in Epsom station and passengers were able to alight onto the platform. There were no injuries caused by the derailment, but minor damage to the train and track.
The immediate cause of the derailment was that two wheel flanges climbed the rail head at a set of points. There were five causal factors and one contributory factor relating to the derailment. The underlying causes were a shortage of track maintenance staff in the area, the lack of proper attention to a defective track lubricator, and not understanding the consequences of a lack of lubrication on that section of track.
RAIB has made three recommendations as a result of their investigation, aimed at:
resourcing of track maintenance in the Wessex area
improving the identification of and response to alignment faults and poor rail condition
providing guidance on the use and siting of rail lubricators.