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Science & technology | Trainspotting

Keeping trains apart is crucial to safety

A new way of doing so uses magnetic signals in the tracks themselves

City train station Hochtaunus Germany
Sep 28th 2022
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Stopping railway trains colliding requires knowing where they are. In
olden days this was done by the handing over between driver and
signalman of a token showing that a block of track was occupied. Now,
automatic devices detect and report a train's passage. But the
principle is the same. Lines in a railway network are divided into
blocks, and only one train at a time is allowed in a block.

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Rationing space this way can, though, lead to inefficiency. More
precise information of each train's whereabouts would permit trains
to travel closer together without compromising safety, and therefore
allow more services to be run. But what might seem the obvious
approach to doing this--to employ the satellite-based global
positioning system (gps) or one of its equivalents--is not actually
suitable. gps is unavailable in tunnels. And where several sets of
tracks run in parallel (for example, at junctions) satellite-based
systems can have difficulty distinguishing which track a train is on,
with potentially catastrophic consequences. But Martin Lauer of the
Karlsruhe Institute of Technology, in Germany, thinks he has an
alternative.

His invention, dubbed the Magnetic Railway Onboard Sensor (MAROS) and
unveiled on September 20th at the InnoTrans trade fair in Berlin,
uses information encoded in the very rails a train is running on, in
the form of something called their magnetic permeability. Employing
this, that train's position on the network can be determined exactly.

MAROS works by lowering a pair of detector coils over each rail and
passing alternating currents through them. These currents are
influenced by the magnetic properties of nearby metal objects. The
production of rails for railways takes care to make them uniformly
strong and smooth, but their magnetic permeability is not among the
specifications. That means a train carrying a MAROS detector picks up
random fluctuations from the rails beneath.

Being random, the resulting pattern of permeability is probably
unique to a given stretch of the network. For a 200-metre section, Dr
Lauer calculates, there is about one chance in a trillion that it is
duplicated anywhere on the 2.3bn kilometres of track currently laid
around the world.

To get the system working on a particular route, a test train rides
it a few times to map out the fluctuations in the rails. After that,
trains running the route would continually compare the permeability
measurements from the detectors with those on the map, and then
report their position to the network traffic controller.

Local changes in magnetic permeability caused by wear and tear or
lightning strikes would show up during routine usage and, once
confirmed, could be added to the map. Moreover, because MAROS
detector-coils come in pairs, the different times that each pass the
same pattern in the track can be used to calculate a train's speed
and acceleration more accurately than the alternative of measuring
the rotation of its wheels, because metal wheels on metal rails
frequently slip.

Dr Lauer's commercial partner, a firm called ITK Engineering, has
been testing the system on scheduled train services plying a 130km
route in Austria and reckons it will be ready for market in 2025. Dr
Lauer himself estimates that using MAROS could increase the capacity
of a busy rail network by 20-30%. It would also cost less than the
existing system of sensors and beacons. #

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This article appeared in the Science & technology section of the
print edition under the headline "Keeping track of the tracks"

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