Lx failure performance

[PJW]

From my studies I am led to believe the performance of lx in degraded modes is specified somewhere.
So how the lx will perform with all anticipated failures.
This is how I have interpreted it.

Thanks

Afraid still not very clear what you are asking.
An AHBC really just has to operate, since a train will be going across that road. Hence all its failure modes are designed to lower the barriers and illuminate boom and road lamps. Operation of various elements are checked within its cycle of operation and if discrepancy is found then barriers are maintained down and failure alarm given to signaller.
Other types of crossing are slightly less critical in that regard as in any failure to operate normally then the train will stop (protecting signal for an MCB, lack of Drivers' Crossing Indicator in case of AOC(L). For these forms of crossings therefore it is generally preferable that level crossing remains open to road traffic.

Most forms of barrier crossing have a Local Control Unit that permits crossing to operated in the majority of fault modes, albeit with very little interlocking.

However I really can't think to what you are referring; it might be helpful for you to quote the reference of what you were studying and then we might be able to make more sense.