The combination of trains and lasers seems like it belongs in a really, really bad network TV adventure series straight out of the late 1970s or something. But no, it’s not Supertrain, because not even lasers could have helped Supertrain. What lasers can help are real trains, traveling on real tracks, that are covered with leaves. Leaves cause way more problems for trains than you’d think, but powerful train-mounted lasers can make everything better.
In the U.K. last year, wet leaves on rails were directly responsible for 4.5 million passenger hours of delays. When trains run over wet leaves, the leaves get shredded and compressed, until they eventually form a hard coating on top of the rail that’s so slippery it can double stopping distances, forcing trains to run slower. The coating also makes it more difficult for trains to get going again (by reducing friction), and screws up the sensors used to control signals. It doesn’t sound like much more than a nuisance, but 4.5 million hours is a lot of wasted time.
The conventional solution to the leaf problem is to outfit trains with nozzles that blast jets of water to try to clean the tracks, or to coat the tracks with sand to increase traction. Neither of these are ideal, since they can damage the tracks or the substrate beneath them. Plus, you have to carry the water and sand along with you.
In the early 2000s, a company called LaserThor thought it might be fun to try laser canons instead:
Testing and on-track trials showed that “the concept of using a laser system is feasible, that a leaf contaminated railhead can be cleaned at 20 mph [32 km/h], and that the laser does not harm people or animals, or affect signaling circuits.” Unfortunately, 20 miles per hour was not fast enough, and vibrations from moving trains caused the laser to bounce around enough that it couldn’t focus on the track well enough to do its job.
A decade later, the technology behind LaserThor has been improved to the point where it can deal with vibrations and operate at speeds up to 50mph. A two-kilowatt infrared neodymium-doped yttrium aluminium garnet (Nd:YAG) laser pulsing at 25,000 hertz can heat up any organic material on the rail to 5,000 degrees Celsius, vaporizing the slippery stuff without damaging the rail underneath. Twenty-millimeter swaths of rail can be cleaned during a pass. The beam offers an added benefit: drying the rails as it clears the detritus, preventing rust.
Dutch rail company Nederlandse Spoorwegen is currently testing the train-mounted lasers on one of its DM-90 trains. They know the lasers work, but two questions remain: Once the rails are cleaned, how long will they stay clean? And how many trains need to get lasers mounted on them to keep things moving? My advice: all of them.
Meanwhile, more Supertrain can be experienced here.
Evan Ackerman is a senior editor at IEEE Spectrum. Since 2007, he has written over 6,000 articles on robotics and technology. He has a degree in Martian geology and is excellent at playing bagpipes.