University of York team set to crack 'leaves on the line'

In a major breakthrough, chemicals responsible for the "black ice" of the railways that often lead to train cancellations in autumn and winter have been discovered.

Researchers from the Universities of York and Sheffield identified the chemical processes that enable leaves to form slippery layers on railway lines - an issue that has long caused chaos for rail passengers and train companies.

Now the team at York University is focussing on enzymes to digest leaf layers on the track.

The University of York (Image: Staff)

Leaves on the line cost Network Rail an estimated £350 million per year in delays for passengers and timetable changes.

The new study, led by Dr Joe Lanigan from Sheffield University’s Department of Mechanical Engineering, deciphered the chemical mechanisms that take place when leaves on the line are crushed between the wheels of a train and the railhead, forming slippery layers that make it difficult for trains to stop and start.

The research team says its findings, published in the journal Proceedings of the Royal Society A, could be used to develop more effective solutions to the long-running issue.

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The problem arises when leaves are crushed against the tracks, forming a layer that dramatically reduces the friction between train wheels and the rails, resulting in what Network Rail describes as the "black ice of the railway".

The researchers focused on the friction and chemical aspects of leaves on the line, providing a new understanding of the processes that happen when leaf matter is present between train wheels and the rails.

The analysis reveals that certain chemicals such as polyphenols, including tannins - the chemicals present in wine and tea, play a "crucial" role in forming a strong, thin film on the surfaces.

Under high pressures and heat, the film contains compounds that stick to the metal surface of the railhead.

The new understanding of the leaf-derived layer's composition is expected to guide the development of innovative solutions to the issue.

Dr Lanigan says that since phenolics play a crucial role, remediation efforts targeting those molecules - such as enzymatic digestion or using next generation cleaning agents that effectively dissolve aromatic species - should be explored.

He believes the potential for cleaning agents to be used as tools for restoring friction to safe levels could ultimately enhance the performance and safety of rail transport for both passengers and operators.

Dr Lanigan said: “The purpose of the research was to find out how tree leaves transform into the low friction black layer that is a problem for railways.

"The biology team at the University of York analysed them from that perspective and here at Sheffield, we looked at the friction and other surface effects."

He added: “The future goal is to use enzymes to digest leaves around railway infrastructure as a green alternative to some of the current solutions which are energy intensive or involve cutting trees down.”

The next phase of the research is to focus on enzymes to be tailored and tested to digest leaf layers on the track.

The team at York is already testing enzymes that can degrade the leaf-derived "black layer" low adhesion films.