Poor drainage caused Watford collision, says RAIB report
THE Rail Accident Investigation Branch (RAIB) says a lack of crest and sub-surface drainage caused a landslip just north of the Watford Slow Lines tunnel that led to a derailment and subsequent collision on September 16 2016.
After hitting the debris, the leading vehicle of London Midland’s 0619 Milton Keynes Central-London Euston (formed of 350264 and 350117) derailed.
It stopped after 380 metres in the tunnel, and was hit nine seconds later by the 0634 Euston-Birmingham (formed of 350233), which following a brake application was travelling at about 34mph.
The right-hand cab doors of both trains were torn off during the collision, and the leading vehicles of both trains were damaged. The driver and two passengers on one of the trains involved were injured.
The RAIB investigation found that above the part of the cutting affected there was a topographical water concentration feature. The resulting flow of water over the top of the cutting, possibly combined with sub-surface flows, caused a washout failure of the cutting slope. RAIB concludes that this water concentration feature was not recognised as a significant risk.
It also found that Network Rail staff responsible for the management of the earthworks were unaware that a serious landslip had occurred very near the same location on February 4 1940, resulting in one death and six injuries.
The London Midland & Scottish Railway built a large masonry face wall to buttress and protect the slope, and a drainage path to allow water to drain safely to track level.
RAIB says drawings of this and the purpose of the face wall should have been identified in the early part of a slope protection project, which had sought to stabilise the cutting slope.
The actions of the train crews involved were praised, with the RAIB concluding that their prompt actions helped to mitigate the potential consequences of the accident. Furthermore, components on both bogies of the 0619 train helped to reduce the obstruction of the adjacent line by engaging the right-hand rail between a gearbox and traction motor.
However, the investigations also found that emergency equipment - including track circuit operating clips, detonators and flags in the cabs of both trains - came loose during the impact, which could have injured the drivers.
NR’s operational processes for dealing with localised extreme rainfall were criticised, as the lines in question were not included in the London North Western Route’s list of earthworks at risk in adverse weather.
A lack of road access for emergency services in the north end of the tunnels was also highlighted. RAIB says this was not identified in NR’s Watford Tunnel emergency plan, nor easily managed by the Fire and Rescue Service.
RAIB recommends that NR should implement measures to improve surface drainage in the area of the 2016 landslip, and review and (where necessary) improve processes for identification of localised water concentration features.
The Rail Delivery Group (RDG) and RSSB (Rail Safety and Standards Board) should commission research into ways in which guidance can be provided to derailed trains, including: the design of bogies and bogie-mounted equipment; how infrastructure features could achieve the same effect at highrisk locations; potential design requirements for the retention or enhancement of such features on trains or infrastructure; and the potential drawbacks and benefits of such measures.
Should the research identify potential improvements, the RDG and RSSB should share the information with the relevant Standards Committees, and record and disseminate the design requirements with a view to their incorporation into future standards.
Siemens and the rolling stock leasing companies should review