Ok, so if cost is no object, then a trunking system should never bog down under the traffic load. Additional frequencies and repeater sites are the cure to traffic congestion!
I guess that would hold true for conventional systems as well.
Yes and no. There's a limit to the number of channels a trunking system will support. While this limit varies according to what specific type of system generally the limit is about 20 channels per system. This limit may allow hundreds (if not more) independent talkgroups, but no more than 19 (19 talk channels + 1 control channel) can be transmitting at any one point in time. Once one stops transmitting, another talkgroup can now utilize that available frequency pair so it may appear to the user that many more are available and active at any one time.
Unless you have some very long winded people (or one fool that likes to play DJ and transmits songs from his iPod over a channel) the system can easily handle many more active channels than there are actual voice paths on that system. Often these systems have a priority assigned to each channel so when no voice paths are available for a high priority talkgroup, a low priority one will be bumped off to allow the high priority one to takeover the channel. One example may be the PD may have a high priority given to their channels while the library cleaning crew may have a very low priority given to theirs. When the system is full, your library radio will beep (telling the user that they lost signal) and the PD officer will get the channel.
With a well designed system, this channel takeover will be a very rare event. In most cases, there should be an available channel. If this isn't a rare event, the system managers should look at the system to see how they can split it up to prevent or at least reduce the number of "bonks". Perhaps even adding a second system so the users are split up among them to help spread the channels around. If you look at some of the large state-wide systems, you may see multiple sites in a fairly small area (but a highly populated one) while others may have only a single site for a large rural area. This is often to keep the many users in the urban area from getting "bonked" while the rural users probably never do.
Conventional systems are always one frequency (or frequency pair if it uses a repeater) per channel. Every user on that channel uses the same frequency. If they need to move to a different channel, they will also move to a different frequency. Trunking systems break the one frequency per channel design and the system and user radios translate the talkgroup request into a temporary frequency assignment on that system. Once the transmission is complete, the system returns that talkgroup into an idle state and allows that frequency to be assigned to another talkgroup when needed.
