In trunked systems the priority will only work on the intended talkgroup if it is also setup as priority in the actual radio system.
For 911 that will be police and fire dispatch talkgroups, other talkgroups can be as well in systems, that is the case for my area.
Be sure of course to set at the Edit Sys Option and turn on Priority ID Scan.
To check if others are also set as priority, if you know a talkgroup is active, you can set that as priority, then press HOLD and rotate the silver knob to another talkgroup. If the radio jumps over that talkgroup, then it is setup as a priority.
So while you can set a priority on any talkgroup, like a public works type, dont expect it to act as a priority.
When two or more priority talkgroups are active, the Unidens will go with the lowest talkgroup number one.
See
Priority Channels