The problem is caused by an estimated 50m leaves falling onto railway tracks every autumn, before being compacted into a smooth, slippery layer by trains. The vehicles can lose their grip on the slick layer of leaves so drivers slow down to compensate, braking earlier and accelerating more gently to avoid wheel spin. Signalling systems can also be affected, as the electric currents used in tracks to detect trains are often affected by leaf contamination, leading rail companies to leave longer gaps between services.
The result is delays, cancellations and timetable changes for passengers, and annual costs of about £345m for the rail industry.
Current solutions include applying sand directly into the contact between the wheel and rail from an onboard system, and track cleaning using high-pressure water before the application of a gel containing sand and steel grains.
Researchers from the University of Sheffield are developing a new efficient solution that could be built directly into passenger trains and cover more track, offering a sustainable approach to the issue.
The new method uses a stream of supersonic air to blast pellets of frozen industrial by-product carbon dioxide – dry ice – at the rail head, freezing leaves and making them brittle. The pellets then turn back into gas, increasing in volume and blasting leaves from the line.
“Unlike current methods, which apply sand directly to the rail, the new solution doesn't leave any residue on the line, meaning there is no damage to the rail or wheels of trains,” a spokesman told Professional Engineering.
The stopping distance of a train is mainly determined by the friction between the wheel and the rail itself, called adhesion. Low adhesion causes longer stopping distance at speed.
On-track trials at Long Marston in Warwickshire showed an improvement in braking performance when the dry ice was applied directly to the wheel-rail interface, the spokesman said. The spokesman also reported that tracks cleaned with dry ice gave a “much better” braking surface.
The technique “will provide more predictable braking and traction than current technology, and will help to improve train performance, reduce delays, increase passenger satisfaction and support the use of new technologies to enable greater network utilisation of the UK’s railways,” said Sheffield mechanical engineer Professor Roger Lewis.
The technology, developed in collaboration with Icetech Technologies, is being trialled again this autumn at sites around the UK. Network Rail is reportedly interested in the results, as is Supertram in Sheffield.
The research was funded through a Small Business Research Initiative call and by the Rail Safety and Standards Board, Arriva Rail North, Network Rail and the University of Sheffield.
Other researchers are also developing on-train technology to tackle leaves on the line. Earlier this year, CoCatalyst received funding from the Department for Transport for its system using water.
Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.