Leaves on the line really are dangerous, and now scientists know why

For decades beleaguered rail bosses have endured ridicule from passengers for insisting that ‘leaves on the line’ bring significant disruption to train services. Scientists at the University of Sheffield found that chemical tannins in leaves react with iron rails to form a slippery black goo which can turn tracks into the equivalent of an ice rink. “Every autumn rail networks across the world suffer delays, accidents and schedule changes due to low friction problems caused by leaves landing on the rails,” write first author Dr Michael Watson, of the University of Sheffield in the journal Proceedings of the Royal Society A. “These leaves form a layer that can reduce the friction between the wheel and the rail to a similar level as that between ice and an ice-skate.” Rail companies call the problem ‘slippery rail’ or ‘low railhead adhesion’ which can lead to wheels slipping and sliding during acceleration and breaking.