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In-Depth Information
Complementarity between Axle Counters and
Tracks Circuits
Marc Antoni
SNCF, Direction of Infrastructure,
Head of the Technologic Innovation Department, Paris, France
Ing. CNAM & SUPELEC, Dr.Ing TUBS, FIRSE, SNCF Expert
(+33)1 53 42 22 52,
marc.antoni@sncf.fr
Abstract. The infrastructure manager choice of type of the track
vacancy detection system requires to be based on a safety and sig-
nalling functions analysis and not on a dogmatic position. The paper
aims at showing that the two main families of these systems are com-
plementary, each of them responding to particular needs in regard to
the route category, the tra
c duty and the accepted risk.
Keywords: Axle counter, Track circuit, System Safety Analysis, Level for
Digital Systems, Railways Critical Systems
1
Introduction
The development of any signalling system uses a whole of “track inoccupancy
detectors”. These functions have to be developed at the SIL4 level. Two main
technologies are used today: axle counters (AC) and track circuits (TC). The
other detection modes generally suffer from lower accuracy, reliability and
speed. Any experts have suggested retaining one of these two solutions as
the unique target system in the Euro-pean standards (TSIs). The aim of
the paper is to show why the decision to impose a unique solution in the
'target system' must not be taken without an in-depth systems approach.
This analysis has to consider the signalling functionalities, the maintenance
principles and the risk acceptance of each country. It seems useless to oppose
the two systems: they are complementary and not interchangeable. It is a fact
that the signalling functions (including degraded mode, safety rules. . . ) are
closely dependant on the nature of the sensors, the change of which can lead to
unsafe situations. The infrastructure managers use comprehensive inspection
procedures to prevent disruptions in operation and hazards due to defects
in the track superstructure. The corresponding procedures are specified in
the rules and regulations. The considered necessary effort for the inspections
is selectively adapted in accordance with the track duty in terms of trac
density, axle load and speed, and the type of track vacancy detectors. It
is naturally greatest on high-speed lines and predominantly characterized
