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science

Leaves DO cause problems for trains

Published måndag 25 oktober 2010 kl 10.05
Crushed leaves turn to oil-like substance

"Leaves on the line". You may think it is just another excuse by train companies to make up for their poor performance and delays. But you'd be wrong, because according to Swedish scientists, leaves falling on train tracks really do cause problems for trains.

We've all been there, standing on a station platform, only to hear an announcer apologize for the delays caused by leaves on the line. And I'm sure we've all raised an eyebrow. How can the annual falling of leaves mean that trains get delayed?

Well, according to Stockholm's Royal Institute of Technology, the fallen leaves really do cause problems, turning into a slimy, slippery mess when they have been run over a few times. Ulf Olofsson is a Professor at the Department of Machine Design, and he's been looking into the issue.

Professor Olofsson likens the leaves to motor oil once they are crushed. The elements in the goo react with the metal of the rails to form a thick black substance, similar to the oil. In fact, many of the elements present in the fallen leaves, are the same as in motor oil. And it doesn't take long for the reaction to start, the leaves need to be run over just 20 to 30 times for the process to begin. And when the rails are covered with the black slime, the train wheels lose friction, and need a much longer distance to brake. The wheels can also overheat if they skid along the tracks, deforming them and meaning the trains have to be taken out of service.

The trains then have to have to travel slower to reduce the risk of skidding. And despite the fact that the leaves do fall from the trees every year, scientists have not found out why they form the slimy mess on the tracks, until now. In co-operation with Stockholm's Local Transport Authority, Professor Ulf Olofsson and his colleagues have found what they think is the answer. And finding the reason behind the slippery tracks, means they now know better what they have to do to deal with the problem.

Speaking to Swedish Radio news Ulf Olofsson says now they know about the chemical reaction between the leaves and the tracks, this means that they know more what they have to do to prevent it. And that means cleaning the tracks much more thoroughly than was previously thought necessary. There are also proposals to install instruments on the trains that will detect the leaf slime, giving drivers warning before it is too late and their wheels deform, meaning delays and that we passengers have to wait at the platform for the next departure.

Our journalism is based on credibility and impartiality. Swedish Radio is independent and not affiliated to any political, religious, financial, public or private interests.
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