These techniques involve selecting circuits in the opposite preference order, ensuring that the highest numbered line, which is typically the last choice for incoming calls, becomes the first choice for outgoing calls.
Common practice is to have the PBX use descending channel selection, and the carrier to use ascending.
For old, analog PBX trunks, glare can be reduced by using ground start signaling, which offers a better answer and disconnect supervision.
Long Distance exchanges in the 1950s and 60s incorporated Glare Detectors to alleviate the problem.
This article incorporates public domain material from Federal Standard 1037C.