'Leaves on The Track' Phenomena Explained

How is it possible autumn leaves can cause such huge disruptions to rail services in the UK?
Jessica Miley

If you have traveled on trains in the Uk you will have probably heard the announcement ‘apologies for the delay, there are leaves on the track’. It sounds ridiculous that autumn leaves could hold up a vehicle as big as a train.

But in this educative video from Steve Mould we learn that even a few leaves can lead to serious consequences for a high-speed train. To demonstrate, Mould straps on some ice skates and measures his stopping distance under different conditions, dry, wet and with leaves on the stopping surface.

Incredibly the stopping distance is about double that when there are leaves on the ground. But why?

After further research, Mould discovers the problem with leaves on the track is actually pretty scientific. When the leaves fall on the track, they are crushed by the trains crossing into a thin layer.

The leaves then release a substance known as pectin which in turn reacts with ions in the tracks forming a tight bond. In dry conditions, this isn't a problem, but when it rains, the pectins soak up the water and form a slippery gel.

Think about it like a shaving strip on a razor. When Mould tested this in his own experiment he found that his stopping distance increased tenfold when the stopping area was covered in a thin layer of wet pectin-rich gel.