Two passenger trains crashed at tunnel mouth

UK watchdog says seasonal factors significant in Salisbury crash

the potentially disastrous crash at Salisbury in 2021 (RAIB) Image released from RAIB report

Britain’s Rail Accident Investigation Branch (RAIB) has published its findings and recommendations regarding the serious collision between two passenger trains near Salisbury in southwest England almost exactly two years ago. Wheel adhesion, brakes, visibility, weather, and extreme leaf contamination in the shape of a fallen tree, all played a part in the crash, at the mouth of a tunnel on approach to the city’s station.

The official safety watchdog for the network, which oversees all rail-based operations in the UK, has made a number of recommendations in its report, examining the collision at Salisbury Tunnel Junction, Wiltshire, in the southwest of England, on 31 October 2021. The RAIB has made ten recommendations, seven of these are made to Network Rail, the national infrastructure agency, and one each to the train operator; the representative Rail Operations Group; and the rolling stock leasing company.

Potentially far more serious collision

It is legislative practice for the RAIB to investigate and report on all incidents on the UK rail network. In its summary on the events of 31 October 2021, the RAIB notes that a South Western Railway passenger service from London Waterloo to Honiton, passed a red signal and collided with the side of a Great Western Railway passenger service from Portsmouth Harbour to Bristol Temple Meads. Both trains were on approach to Salisbury, an important junction and railway hub, also much beloved by Russian tourists for its celebrated cathedral. The collision, at over 50 miles per hour (80 kph) took place at Salisbury Tunnel Junction, which is on the immediate approach to Fisherton Tunnel, under the city’s eastern suburbs.

The impact of the collision caused two carriages in each train to derail. Both trains continued some distance into Fisherton Tunnel before they came to a stop. Thirteen passengers and one member of railway staff required hospital treatment. A potentially far more serious collision involving a train travelling in the opposite direction was avoided by less than a minute. “This was a very serious accident and the first time since our inception in 2005 that RAIB has investigated the collision of two passenger trains travelling at significant speed”, said Andrew Hall, Chief Inspector of Rail Accidents. “The risks associated with leaves being crushed onto the top of rails by the pressure of trains’ wheels, resulting in a slippery layer, is very real and long known.”

Increased density of vegetation

The RAIB put the primary causes of the accident down to track adhesion conditions, which the report describes as very low. “The driver of train 1L53 [London-Honiton train] applied the train’s brakes, [but] not sufficiently early on approach to the signal protecting the junction to avoid running on to it”, says the RAIB. “The braking systems of train 1L53 were unable to mitigate this very low adhesion.”

The level of wheel/rail adhesion was very low due to leaf contamination on the railhead, says the RAIB. This had been made worse by a band of drizzle, a typically British fine rain not unlike a persistent mist spray. This leaf contamination resulted from the weather conditions on the day of the accident, coupled with an increased density of vegetation in the area which had not been effectively managed by Network Rail’s Wessex route. The safety report also found that South Western Railway not effectively preparing its drivers for assessing and reporting low adhesion conditions was a possible underlying factor. Two issues were found relating to the severity of the consequences. These were a loss of survival space in the driver’s cab of train 1L53, and the jamming of internal sliding doors, which obstructed passenger evacuation routes.

Seasonal management and design changes recommended

Since the accident, Network Rail has reviewed its training for off-track staff at network level, and its adhesion management standards. The infrastructure agency is also reviewing its arrangements for proactively responding to reports of low adhesion, including how it undertakes railhead treatment. South Western Railway has made changes relating to the training and briefing of its drivers on autumn arrangements. Both Network Rail and South Western Railway have jointly updated their annual autumn leaf fall working arrangements. The Rail Safety and Standards Board (a separate body representing the industry) has revised the standard that provides guidance for the rail industry regarding the management of low adhesion.

Diagram of Salisbury crash 2021
Diagram of Salisbury crash in 2021 (RAIB)

The RAIB recommendations include proposing that Network Rail review the processes, standards and guidance documents relating to the management of leaf fall low adhesion risk; the training and competence of staff dealing with vegetation management and seasonal delivery; responses to emerging and potential railhead low adhesion conditions; management of railhead treatment regimes; assessment of the risk of overrun at signals which have a site at high risk of low adhesion on their approach; and a review of the retrospective application of design criteria for the Train Protection and Warning System. A recommendation to South Western Railway urges a review of arrangements for training and briefing drivers to identify and report areas of low adhesion. The Rail Delivery Group has been asked to consult operators and the RSSB over technologies other than sanding systems and wheel slide protection to improve braking in low adhesion conditions. Finally, the rolling stock leasing agents and owners – Porterbrook, Eversholt and Angel Trains have been asked to look at the design of the internal sliding doors on class 158 and 159 carriages – some of which jammed in the incident.

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Author: Simon Walton

Simon Walton is UK correspondent for RailTech.com and Railfreight.com

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