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by shorter inspection intervals. Rail defects arise from a wide range of root
causes, up to and including rail breakage. On CWR modern tracks, most
of broken rail (BR) situations can be safely detected via track circuits (in
France,aBRpresenting2
Ω
serial resistance is detected by actual HSL track
circuits). Moreover, in many countries, such BR has to be normally reported
by the locomotive driver to the operating department via the on-board train
radio link today. Generally, the entire set of rail maintenance guidelines does
make a distinction between lines with axle counters and lines with track
circuits detecting BR: the inspection effort required is consequently greater
in the first case. It's an infrastructure manager's choice with a probabilistic
or deterministic safety points of view and a global life cycle cost and in regard
with the trac of the lines.
2
Technical presentation of the TC and the AC
Nowadays, the systems of train detection are very important products, abso-
lutely essential to ensure the safety of the railway exploitation. The two basic
principles of the detection and localization of trains are track circuits (TC)
and axles-counter (AC).
Track circuit principle: a transmitter emits in the track through the two
rails an electric coded current which is received at the other end of the track
section by a receiver. The track circuit contributes effectively to the train
detection and the safety of their movements. In many countries, such as
Belgium, France, Great Britain, OSJD countries, Korea the United States or
Japan, track circuits are the predominant sys-tems used for train detection
providing the signalling system with the locations on the network of any
train, and any railway vehicle, it any moment and in full safety. The TC length
domain, determining the accuracy of the detection, ranges from 22,5m to 3km,
for example France. In most of the countries listed above, HSL track circuits
don't need insulation joints in the direct way and their proper functioning is
checked by commercial trains using a ground to board transmission. Broken
rail detection is as well a safety function ensured by the TC
1
, in particular on
high density lines. Some TC
2
makes it possible to detect safely and localize
a broken rail in a 30km section.
Axle-counter principle: axle-counters compare the number of axles enter-
ing and leaving a considered track section. From this calculation results that
at any moment the device associated with the track section knows the number
of axles present in the zone, to avoid having more than one train at the same
time between the two detec-tors. If the in/out difference number takes any
value other than zero ( 1 in some countries), the track section is considered as
“occupied”; if the number of axles added up for the track section is null then,
obviously, the track section is considered as “free”. The detection points count
1
In any countries it's an safety obligation to detect BR (France, Belgium ...), it's
not the case for any other counties (Germany, UK...)
2
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