If you’re anything like us, gravelly-voiced train announcements which claim delays are down to “leaves on the line” prompt splutters of disbelief. Leaves on the line? Is this code for “We’ve not only messed up our scheduling, we couldn’t even be bothered to put any effort into making up an excuse”?
It turns out, however, that “leaves on the line” are a huge problem for rail operators. Last year in the UK, according to National Rail figures, the innocent-looking bits of biomass accounted for 4.5 million hours worth of delays. That’s because leaves, when wet and under pressure from train wheels, form a very thin, very slippery layer on the rails. This layer slows down braking systems (you don’t have to know much about trains to know this is not ideal) and can block electrical signals in the rails from tracking the trains properly.
Train operators have tried spraying water from the front of trains to remove the caked-on leaves without stopping service, but this is, for the most part, ineffectual: generally, removing the leaves has required the help of a special “descaling team”.
Now, however, researchers from Delft University have hit on a new tactic which they believe could keep the lines clear and end delays: using lasers to zap away the leaf layer.