General Information on Track Circuits - RGS Online

<strong>General</strong> <strong>Information</strong> on Track Circuits
9 Track Circuit Gaps
and Staggered
IRJs
10 Selective Operation
of Track Circuits
11 Bad Rail Surface
Withdrawn Document
Uncontrolled When Printed
Railway Group Approved Code of Practice
GK/RC0752
Issue Two
Date December 1998
Page D9 of 20
It is essential that all classes of vehicle, irrespective of wheelbase arrangement,
are detected by the track circuiting, otherwise false track circuit clearance may
lead to premature movements of points or irregular release of signals. Based on
the dimensions of existing rolling stock and allowing for future developments, the
following shall apply:
a) The maximum dead section between two track circuits in areas of
continuous track circuiting is 2.6m. This is the minimum wheelbase of
vehicles working unattached.
b) Opposite IRJs must be regarded as the ideal arrangement. If unavoidable,
physically staggered overlaps between nominally opposite IRJs must not
exceed the following limits:
Non–electrified areas 2.6m
Electrified areas if the traction rails overlap 2.6m
Electrified areas if the insulated rails overlap 2.1m *
Isle of Wight lines 1.7m *
Note*: These distances are stipulated by the Electric Traction Engineer to
prevent a motor bogie losing its negative return path (see Figure D12 for
clarification).
a) There must be at least 18.3m between the nearest joint of any physically
staggered pair and an IRJ defining a clearance point at the end of the track
circuit. Where this cannot be obtained, special sequential controls must be
provided.
b) If the physical stagger exceeds 1.6m, there must be at least 18.3m between
the nearest joint of the staggered pair and the next IRJ. If the stagger is less
than 1.6m, this distance may be reduced to 11m. Where the requirement
cannot be met, special sequential controls must be provided.
c) Full details of critical dimensions for train detection are contained in
GK/RT0011.
Operation of a portion of a track circuit by the selection of the positions of a set
of points is not permitted. Such portions must be separately track circuited.
At locations where oil film or rust is excessive, (eg. traction depots, terminal
platform lines, etc), a stainless steel strip can be applied to the surface of the
running rail by the Permanent Way Engineer. This must be shown on bonding
plans, using the symbol specified in Part C. The vibration caused by the
resulting uneven rail surface restricts its application to very low speed
applications (5 mph maximum).
Alternatively, the GEC Alsthom High Voltage Impulse (HVI) track circuit may be
used (see GK/RC0756).
12 Emergency
Crossovers Where a crossover is clipped and padlocked or worked from an adjacent ground
frame and subject only to an emergency release, track circuiting is not required
for movements over the crossover.
RAILTRACK D9