Overcoming leaves on the line

Source: RTM April/May 2018

Paul Gray, professional lead of engineering R&D at the RSSB, explains how latest research proves using double variable rate sanders on trains dramatically reduces braking distances.

Low adhesion conditions cause an average of 350,000 delay minutes each year and can result in station overruns and signals passed at danger. This challenge goes beyond autumn: it is a fact that low adhesion affects the railway all year round, making braking distances in some situations unpredictable. This not only negatively affects today’s railway operations but also the industry’s aspiration of running more trains per hour. 

Sanders are routinely used on trains to blast sand between the wheel and the rail to reduce the impact of slippery rail head conditions. RSSB has designed and delivered research with industry partners to find out how the rail sector can best optimise the use of sanders in low adhesion conditions to improve services for passengers, enable better performance, and deliver higher capacity. 

A three-month programme of full-scale testing at the Rail Innovation and Development Centre at Melton Mowbray, using two new Class 387 trains loaned by Great Western Railway, was carried out generating a robust dataset from over 220 test runs with various configurations of sanders, test speeds and train formations.

This research has proven that changing the approach to sanding by introducing double variable rate sanders, which automatically apply more sand when braking at higher speeds, dramatically reduces braking distances and can provide assured 6%g braking performance. In fact, it was found that using double variable rate sanders can improve stopping distances on a four-car train by around 50% compared to a single fixed-rate sander.

These are game-changing findings because they demonstrate how existing technology can be deployed more effectively to overcome the ‘leaves on the line’ problem and year-round delays caused by poor adhesion. Moving to double variable rate sanders will reduce low adhesion-caused delays, platform overruns and signals passed at danger (SPADs). Also, it will improve the consistency and predictability of train braking, a key enabler to increasing capacity.

Overall, the results revealed:

  • Using double variable rate sanders improves braking significantly compared with the current fixed-rate sander configuration. Using double variable rate sanders can improve stopping distances on a four-car train by around 50% compared to a single fixed-rate sander;
  • Double variable rate sanders can provide assured 6%g braking performance, an important braking performance measure as it is the basis for timetable planning;
  • Using double variable rate sanders can reduce SPADs and platform overruns due to low adhesion conditions by over 90%.

Two dedicated briefing events were held in February to bring the industry together to discuss the findings and explore opportunities and barriers to adopting the new recommended sander configuration from autumn this year.

RSSB has stated its commitment to helping the industry implement these compelling findings, and is ready to offer the knowledge and experience of the project team together with seed funding for early adopters who are prepared to fit double variable rate sanders to some multiple units from autumn 2018.

Passengers expect trains to run on time, and these results will help operators to do just that by running a more reliable service regardless of weather conditions. 

The research improves our understanding of how existing sanding technology can be used much more effectively to combat poor rail adhesion. This longstanding issue affects millions of passengers each year, preventing the delivery of the efficient and reliable service they expect.


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