Here i what I have applied in my experience:
Talking about Trunks:
Amount of traffic that is carried in reference to the traffic capacity with Erlang B, example:
1 E1 suports 1240 minutes (G.O.S = 0.01), your traffic measurement shows you 800 minutes during busy hour, it means 65 % of traffic utilization.
Amount of calls that can be stablish during the busy hour, no matter the holding time it supports. it is more related to software capabilities than capacity.
Lets say the same E1, using PRI signaling and R2 signaling, PRI is faster than R2 signaling therefore although both supports the same traffic they have different perfomance.
Hope it helps you cab email me for further information: