Permissive signals in one directions

This older concept allows reverse main running but with a limited volume. Only the left hand track has permissive signals, the right hand is equipment with a distant signal for the main signal. Only one train at a time is allowed to run contra flow.

Basic line lay-out

An example of normal flow

A train is signalled between the two stations

The distant signal doesn't change state even if the block is occupied

The station entry is cleared

An example of contraflow

A train is signalled between the two stations

The station entry is cleared