Engineers in the Netherlands are experimenting with a highly innovative approach to dealing with the problem of track-strewn leaf debris, with a method that sounds akin to something straight from the pages of a work of speculative science fiction.
Keeping tracks free of fallen debris is one of the most besetting problems that railway operators face on a regular basis. This is particularly the case for the leaves that tumble onto fall lines in tree-lined areas, as the fallen foliage can create highly hazardous track conditions.
When trains running on railway lines squeeze and compress the fallen leaves, a stiff yet slippery residue is produced that reduces wheel friction and grip and affects key processes such as acceleration and braking.
The resulting diminution in contact between wheels and tracks is also particularly hazardous, given that it can influence the signalling systems whose role is to prevent train collisions.
Removing these leaves to ensure the safety of railway lines is a major source of inefficiency for modern railway systems. Data produced by the UK’s Network Rail indicates that leaves on tracks were responsible for a staggering 4.5 million hours in passengers delays during 2013.
Dutch Railways is trialling the usage of Laser Railhead Cleaners (LRC) developed by researchers from Delft University of Technology in collaboration with Strukton Rail.
The LRCs are downward-pointing lasers installed to the fore of train wheels which vaporise any accumulated leaf residue on the tracks as the vehicles glide over them.
The lasers are capable of cleaning 20 millimetres of railhead on either side of the track while trains are moving at speeds as high as 80 kilometres per hour.
In addition to destroying any existing debris, the lasers dehydrate the rail surface to help prevent the subsequent accumulation of fallen leaf matter, while also scrubbing off any build-ups of rust.
The laser-cleaning method was first proposed in 1999 by British company LaserThor, which produced a train-specific laser gun that was capable of firing as many as 25,000 times a second and reaching temperatures as high as 5000 degrees Celsius.
When Network Rail installed the device on their trains, however, they found that its effectiveness was severely impeded by the vibrations of the moving vehicles, which disrupted the accuracy of the laser. Network Rail eventually gave up on the approach, turning instead to high-intensity water jets as the best expedient for keeping its tracks clean.
The developers of LRC believe they have solved the problem of these disruptive vibrations by developing a system that temporarily shuts down the lasers whenever the motion of the train threatens to throw off their accuracy.
The system also possesses a triple suspension system that helps to protect the optics, and ensure its precision.
A sophisticated Track Circuit Monitoring System further heightens the efficiency of the system by using an in-house POSS system to assess the condition of the rails. The system can determine when leaves are present by measuring the electrical resistance of the track, enabling the materials to be lasered off well in advance of heavy accumulation.
Should the Dutch Railways laser trial prove to be a success, the devices may rapidly emerge as the preferred method for keeping railway tracks clean.
The lasers possess numerous advantages compared to conventional water-based cleaning methods. They do not require frequent refilling the way water tanks do, and more importantly they do not cause damage to railway tracks and the underlying substrate the way high-powered water jets can.
Malcolm Higgins, the founder of LaserThor as well as a consultant for the Dutch trials, said high-powered lasers installed on the trains will leave the tracks themselves unscathed because of their specific wavelength of 1064 nanometers.
This wavelength can be absorbed by organic matter such as leaves and oils, but is simply reflected away by the metals used to build modern railway tracks.