NR SSIDIS166 ISSUE 2 PDF

INTRODUCTION

Permissive and non-permissive shunt routes have substantially different controls. For example, non-permissive routes are required to set and lock an overlap, and to prove the exit signal alight. Permissive routes on the other hand are required to prove the previous move at a stand, and to lock the exit signal to prevent th e train ahead from moving off.

Whereas separate Main and Call-On class routes are provided for non-permissive and permissive moves from main running signals, independent shunt signals usually have just the one Shunt class route which can work in both permissive and non -permissive modes, depending on the conditions appertaining at the time of route setting. This has led to considerable difficulties in control table presentation, where the (S) class route may or may not lock various functions depending on the conditions at the time the route was set. It has also led to complexities in SSI data, where different locking and aspect conditions h ave to be applied, depending on whether the shunt route is working permissively or non - permissively.

On the Southampton Area Interlocking Renewal (SAIR) project, the control tables present permissive and non-permissive shunt routes as completely separate entities, as (P) and (NP) class routes. Network Rail have instructed that they should likewise have completely separate (P) and (NP) route identities in the SSI data.

Network Rail's Signalling Principles Group are currently considering the nomenclature to be used for permissive and non-permissive shunt routes, so future schemes may use a nomenclature other than (P) and (NP) for control tables and data.