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Fig. 6. The functions
h
(
t
)
, the renewal density of grindable and non grindable rail
defect
We assume that the rail defect and the associated derailment risk is a
dominant factor for the choice of the track inoccupancy and track integrity
detectors.
5
Conclusions
Each technology of TC or AC has its own domain of pertinence. Neither
should be rejected out of hand. In the current state-of-the-art, neither of
the two solutions allowing detecting the presence of trains is perfectly safe;
signalling plant implicitly integrates the possibility of transient failures of the
chosen solution.
The TC, through its occupancy detection function, provides, especially on
high tra
c or high speed lines, a higher level of safety because of lower risks
from human inter-vention, as much in maintenance, particularly corrective
maintenance, as in degraded mode operation. Moreover, it ensures a continual
check of the electrical integrity of the track. The TC's reliability is all the
better when the trac is great and/or that the traction system is electric
(typically
10
−
7
/h/TC on HSL). Moreover, the TC is well suited to trac
increase, since it allows the block to be permissive and sectional release in
signal boxes. With the TC's, the safety level isn't coupled with the track
maintenance policy, in particular regarding grinding.
The AC provides, in France, for low-trac lines, an economical solution to
the con-trol of clearing of long sections, without the risk of deshunting, albeit
at the price of a stricter route locking (absolute block, no sectional release
and so on) and greater operating complexity, in the event of disturbance or
failure. The rate of failure internal rail defect rate is particularly low in this
case.
The preventive grinding has been proven to minimise rail defects, to ex-
tend rail service life, to reduce the maintenance costs of the track but cannot
