Low adhesion can be caused by moisture on the rail mixing with the film produced by ‘leaves on the line’ and is particularly severe in autumn. But low adhesion can occur at any time of year, due to contaminants such as rust or grease. 

Safety risks from low adhesion include signals passed at danger (SPADs), station overruns, and train collisions. Disruption and autumn timetables delay passengers and cost money. Low adhesion is also a barrier to increasing capacity. Being able to stop trains predictably under any adhesion conditions is essential to the safe running of a busy railway.

Solutions for industry

Our response to the adhesion issues affecting the railway is ADHERE: ADHEsion REsearch challenge. Steered by the Adhesion Research Group, this pipeline of research aims to achieve ‘adhesion conditions that are unaffected by, and independent of, the weather and climate’.

Sand and sanders

A range of train-borne mitigations can tackle low adhesion. Sanding is one of the main ones. Our research showed that variable-rate sanders—which dispense more sand at higher speeds­—offer a step change in braking performance. Laboratory and on-track testing proved that these enhanced sanders restore normal braking in low-adhesion conditions. Following these findings, the Key Train Requirements document now recommends that variable-rate sanders are standard on all new passenger rolling stock.

We worked with two operators to support retrofitting of variable-rate sanders. Early analysis shows improved autumn performance in both fleets. We are continuing to promote and support wider adoption.

We are also looking at enhanced sand products, and at the occupational health risks of working with sand.

Low adhesion in freight vehicles

We are investigating the factors that affect freight braking in low-adhesion conditions. This explores freight braking characteristics, environmental conditions, and freight driver policies; and how these differ from braking in passenger trains. We are also undertaking detailed research into the conditions that lead to wheel flats on freight vehicles.

Real-time monitoring

We are working in partnership with Chiltern Railways, Knorr-Bremse, Angel Trains and the University of Huddersfield to trial a novel monitoring system that shows adhesion conditions in real time. The trial should provide Chiltern Railways with insights into the frequency and severity of low adhesion in different conditions. It will also identify low-adhesion hotspots, to help target mitigations.

Decision support frameworks

The industry has a variety of tools to manage low adhesion and its consequences. But what is the right mix of technologies to use in a particular location?

Research is underway to produce guidance on how to compare and assess the effectiveness of different adhesion technologies in the context of specific routes and fleets characteristics.

Making investment cases for adhesion mitigations can also be challenging. The difficulty of justifying investment can lead to ongoing use of existing solutions—even when a new approach might be more cost-effective. Recently completed research has reviewed the financial, economic and social case to improve adhesion, helping managers make the case for action.

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