A sticky situation: managing rail adhesion

The issue of low wheel/rail adhesion has been a global problem since the earliest days of the railways. Making it harder for trains to accelerate and brake efficiently, low adhesion can result in station overruns, signals passed at danger (SPADs), buffer stop collisions, and train collisions and derailments. The 2023 leaf fall season, for example, had 337,700 associated delay minutes. 

Coming to a head every autumn (The most recent figures – from 2019 – cite estimated costs to industry and wider society during this season to be in the region of £355m a year), the issue is often blamed on leaves on the track, but crushed wet leaf film isn’t the only culprit.  

You can’t it’s one of the major causes, but low adhesion can also be caused by water, iron oxide, industrial contaminants or a combination thereof. This means it’s a concern to the industry all year round, especially since these contaminants have the potential to electrically insulate a train’s wheels from the rail, failing to short a track circuit and giving the appearance that no train is present. 

“These incidents are referred to as wrong side track circuit failures (WSTCFs), which compromise system integrity and could result in a train collision or derailment,” says Ben Altman, senior research analyst at the Rail Safety and Standard Board (RSSB).  

Double variable rate sanders 

A number of solutions have been developed to tackle this problem over the years, and one of the most promising in Great Britain is double variable rate sanders (DVRS). 

Most trains on the Great Britain mainline are already fitted with sanders that discharge a fixed rate of sand, but testing by RSSB found that using two variable rate sanders in series could half stopping distances on a four-car train travelling at 55mph compared to a single fixed rate sander.