The laser express (Image: Andre Bernardo/Getty)

IF THEY won’t budge, zap ’em! Train-mounted lasers are being tested as a way of clearing the path for high-speed trains. What requires such forceful removal? Leaves.

Every autumn, fallen leaves are a dangerous problem for railways in much of Europe and North America. Passing trains squash leaves on the track into a hard Teflon-like residue that coats the rails, making it difficult for wheels to grip them. The reduced contact between wheels and track also affects signalling systems that are meant to keep trains from colliding. According to Network Rail in the UK, leaves caused 4.5 million hours of passenger delays in 2013.

Last month, Dutch Railways began trials to zap leaves into oblivion with lasers. Angled downwards and fitted just in front of a wheel, the lasers vaporise built-up residue as the train passes. They also dry the rails to prevent new leaves from piling up. This gives trains better traction, allowing faster acceleration and braking.


Using lasers to clear leaves was first proposed in 1999 by a UK company called LaserThor, which developed a laser with a temperature of 5000 °C that was strong enough to zap leaves 25,000 times per second. “This worked really well in the lab,” says a Network Rail spokesman. But when fitted to moving trains, the vibrations made it hard to keep the laser focused on the rails, he says. Network Rail eventually opted for high-powered water jets instead.

The focusing problem is one thing that the Dutch team has been working on. Their system also briefly shuts off the laser whenever vibrations make it miss the rail.

If they are to get a second chance, lasers will once again have to compete with water jets, as well as jets of a sandy-gel mixture known as Sandite, and manual scrubbing. But lasers have advantages: sand and water tanks need frequent refilling, and water jets can damage the rails and the substrate below.

If they are to get a second chance, lasers will have to compete with jets of water and sand

According to Malcolm Higgins, the founder of LaserThor, who is also an adviser for the Dutch project, lasers will not damage the tracks. This is because their wavelength of 1064 nanometres means they are absorbed by the leaves and other organic matter such as oil, but not by metal, so energy from the lasers is reflected off the rails.

This article appeared in print under the headline “Lasers to blast leaves out of trains’ paths”