scope:

General

The general requirements for interfacing TPWS are given in NR/L2/SIG/10133 (Ref. 1).

Four methods of implementing these requirements for SSI signalling have been adopted, referred to as Methods 1a, 1b, 2, and 3.

The physical interface arrangements for these methods are described in SSI8500D, Section 3.4.

Note that for all methods, the interface with Position Light signals associated with a Main signal (where fitted) will normally be handled in hardware, and the data methods described below are unaffected by the inclusion of such a feature.

The exception to this rule is in complex approaches, where separate control and/or proving of OSS and TSS is employed. Details of the arrangements for complex approaches are described in Section 6.

The following terms are used in the following sections:

TSS Train Stop Subsystem, i.e. the TPWS subsystem controlling the Train Stop loop

OSS Overspeed Subsystem, i.e. the TPWS subsystem controlling the Overspeed loop

SIM TPWS Signal Interface Module, i.e. that part of TPWS equipment to which the control and proving circuits are connected.

Controlling Signal The TPWS equipped signal to which an OSS relates (this may not necessarily be the signal to whose module the OSS is physically connected). Note that a separately controlled OSS may have more than one Controlling Signal, according to the lie of intervening points.

Path A line of route between (typically) an OSS and its Controlling Signal via any intervening points. The term "path" is used as distinct to "route" because the path may exist whether or not a route has been set.

"on" A red aspect

"off" Any proceed aspect (including a position light aspect)

In advance beyond the signal under consideration

In rear on the approach to the signal in question

Note 1: This document is published after the completion of the TPWS retrofit programme. However, for consistency with NR/L2/SIG/10133 and to allow for possible future modification to retrofitted schemes, the Sections relating to retrofit applications are retained.

Note 2: This document does NOT encompass any additional requirements arising from the implementation of NR/GN/SIG/00028 (Ref 2). These will be dealt with fully in a future amendment to the SSI Applications Manual.