Salisbury accident 2021
Fourteen people needed hospital treatment after low adhesion caused a train collision at Salisbury Tunnel Junction.
At around 18:43 on 31 October 2021, a Waterloo–Honiton service struck the side of a Portsmouth Harbour–Bristol Temple Meads. The Honiton, a three-car Class 159, was travelling at 52mph when the incident occurred at Salisbury Tunnel Junction, where the impact caused a collision derailment, both trains ending up within Fisherton Tunnel before they came to a stand.
Thirteen passengers and the driver of the Honiton required hospital treatment as a result of the accident, which was found to have been caused by low adhesion brought about by leaf contamination.
Among the most important weapons provided on rolling stock to combat low adhesion are sanders. The absence of sand in a train’s sand hopper was causal to the two-mile overrun at Stonegate (East Sussex) in 2010. Although perhaps the most obvious reason for good amounts of sand not getting to the wheel/rail, there are also other set-up/maintenance reasons.
Partly as a result of this incident, and many others, RSSB did a lot of work to compare fixed-rate sanders (constant sand delivery rate) and variable rate sanders (sand delivery rate varies with train speed).
Using a pair of variable rate sanders (at two axles), which became known as double variable rate sanders (DVRS), was found to improve stopping distances on a four-car train by around 50%, compared to single axle fixed-rate sanders, even in very low adhesion conditions.
The accident was found to have been caused by low adhesion brought about by leaf contamination.
Working with the cross-industry Adhesion Research Group, RSSB has also developed an ADHEsion REsearch challenge programme, known as ADHERE. The programme has been running since 2018 and sets out to provide new knowledge and capabilities to achieve adhesion conditions that are unaffected by and independent of the weather and climate. The programme has five workstreams:
fundamental science and modelling
driver behaviours
wheel/rail cleaning, (re) contamination and train detection
changes to train design
forecasting adhesion.
Completed project reports are available from RSSB’s research catalogue, and there is a range of projects under way and being planned. One project is taking a closer look at leaf biology and the potential to use enzymes to help break down leaf contamination layers on the railhead. Another project seeks to develop machine learning algorithms to estimate low adhesion conditions using railhead, lineside and environmental data, in order to estimate and compare low adhesion conditions.
RED 66 covers low adhesion, along with the impacts other weather-related conditions can have on train operations.
OTM drivers: Take care when leaving possessions and when driving at night or driving on an infrequently used line. OTM operations often coincide with times when moisture has had a chance to build up on the railhead.
Freight drivers: Check the train’s weight, as lighter trains are harder to slow in low adhesion conditions. Hold back to reduce the amount of power and braking necessary to control your train.
Passenger drivers: If your train is fitted with wheel slide protection (WSP) and automatic sanders, brake to a level that ensures sand is deployed, and allow the WSP to operate. Don’t release or fan the brake when there’s WSP activity.
All images used in this article are courtersy of RAIB.
