Information Technology Reference
In-Depth Information
the number and direction of axles passing the rail contacts and transmit this
data to the ACE who defines the section to be “free” or “occupied”. In case
of an equipment failure, the section will be treated as “failed”.
The reset of the systems: The track circuits have no need of resetting
function. This property is taken into account in the line tra
c organization,
in the exploitation and maintenance prescriptions of the countries using the
TC and in the interlocking & block design. The reset is required to clear
an axle counter section initially for commissioning or when it has become
disturbed, i.e. when there is no train in the section but the axle counter
indicates occupied as a result of a disturbance. Resetting axle counter sections
is a safety-relevant operational procedure, which must be clearly defined in
the operator's and maintainer's regulations.
3
Functional differences and specific Constraints
Detecting the inoccupancy of a track section is a safety-critical function.
It must therefore be performed with a high level of reliability, consistent
with the reliability levels of the other safety functions. Choosing a particular
technology for this function necessarily impacts on the whole system, and
especially the following:
- the methods and means of operation and maintenance of the fixed plant;
- the design of the infrastructure and signalling installations;
- how safety is achieved in nominal operation and in degraded mode;
- the interoperability-related aspects in the sense of the rolling stock-infra-
structure interface, by the imposition of constraints on the rolling stock.
From the standpoint of operation:
It is necessary to consider specific constraints brought by the TC, in
particular that:
- the maintenance vehicles and lorries are automatically detected. It has
to be considered for the exploitation;
- the transit of some particular vehicles on some less circulated and not
electrified track sections (
<
10000
T/day
) can lead to the application of
specific proce-dures;
- the functioning of the automatic blocks systems and level crossings are
not monitored by the operators . . .
It is necessary to consider specific constraints brought by the AC, in
particular that:
- it imposes the absolute block (one train between to detectors), as it ex-
hibits un-safe failure modes in “permissive blocks”, which is used in France
and Belgium (UK and France use recently AC of secondary lines with ab-
solute block);
