Opposing Locking Release

[sadiqameen]

Hi PJW,

Can you please give an insight on this statement "Controls on opposing routes are also sometimes released by the occupation, after time, of track sections" it is little hard for me to understand this statement.

[PJW]

This relates to sectional release of route locking as implemented in the UK and elsewhere. In this the basic interlocking of one route against another route is supplemented by route locking elements for each track section. This is needed to maintain the locking on those portions of the route where it is still needed after the route itself has been normalised as soon as the train has passed the entrance signal.

There are broadly 2 scenarios where the locking is released "after time"

a) a permissive move. A call-on or shunt (permissive) route may be set and the signal clear when there is a STATIONARY train in route. This of course could have come from the opposite direcion, but once stopped this is no longer relevant. Hence the opposing locking is released once the last track in the opposing route has been continuously occupied for sufficient time.

b) where the routes themselves do not utilise any common infrastructure, but the overlap of the first conflicts with either route or overlap of the second. Hence the second route may only be set after the overlap associated with the first route has timed out.

Hi PJW,

Can you please give an insight on this statement "Controls on opposing routes are also sometimes released by the occupation, after time, of track sections" it is little hard for me to understand this statement.