HomeRail NewsRSSB Sponsored Double and Variable Rate Sanders Trial: The Results

RSSB Sponsored Double and Variable Rate Sanders Trial: The Results

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In November 2017, Rail Engineer reported on tests sponsored by RSSB being carried out at RIDC Melton to evaluate the use of both sanders on more than one wheelset on the train, and sanders that can deliver sand at a variable rate with the aim of providing more dependable braking in challenging adhesion conditions. Results were due in early 2018. On 6th and 7th February, the results were presented to the industry.

The Adhesion Research Group (ARG) had challenged developers to provide solutions that could achieve a braking rate of 6%g (0.6m/s2) in challenging adhesion conditions. If successful, the following benefits could be delivered:

  • No need to adjust schedules in the autumn
  • Virtual elimination of adhesion related SPAD incidents
  • Virtual elimination of adhesion related platform over runs.

It would also contribute to the Rail Technical Strategy objectives of running trains all year round “timed and delivered to the second” and “closer together”.

The results were transformational and offer the potential of a step change in performance; certainly the ARG’s challenge was delivered during the tests. A gross summary below of the very detailed and complex results highlights the benefit.

For braking in “step 3” (0.9m/s2) demand from 55mph on low adhesion rail with an untreated friction level of 0.02 (very challenging), the following stopping distances were recorded with sand applied continuously throughout the stop:

  • No sanders: >1200m,
  • Single, axle 3, fixed rate sander: 800m (the current good practice for most modern trains),
  • Two fixed rate sanders: approx. 650m,
  • Single variable rate sander: approx. 600m,
  • Two variable rate sanders: 400m.

Put simply, putting down more sand in the right places halves the stopping distance compared with today’s current good practice.

The challenge is now to encourage the industry to adopt the results and work rapidly to develop modifications to existing and new trains to implement the findings. There’s a lot of benefit, and the industry estimates that autumn adhesion problems cost the industry nearly £350m per annum.

Read more: On board ScotRail’s new Class 385



  1. The testing is carried out at 55 mph. The coefficient of static friction decreases with speed, so what happens when braking from 125 mph? Additionally the air flow around the sand nozzle, will surely be different at higher speed, how will this influence sand distribution?


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