Curious as to the variants that exist in relation do automatic half barriers.
In particular what variants are in use that are not monitored from a signal box/signalling centre.
Are there variants which are locally monitored (ie white light)
Are there variants that are designated as driver monitored, if so what is the difference between these and local monitoring ?
Are there variants where the white light is placed some distance on the approach to a crossing ?
Do AHBs normally fail with the barriers up or doen in the event of power loss ? Is there different behaviour for different variants ?