Yes, Mike. I've noticed this too. Back when I lived in MD, Howard County Fire & PD units had a channel 4 also. Its purpose was for coordination between pd and fd units. Most often in that configuration the PD units would use it for running license, wanted and registration checks, although the FD could switch over to it if they had multiple incidents and needed a fireground channel, or actually use it for its original intention. Years later, after the county had grown, they split the county into two police districts and assigned channel 4 as the southern district police dispatch channel exclusively. Baltimore County, MD also has a Fire/PD coordination channel as do other jurisdictions on their respective TRS'. Unfortunately, communications on those talkgroups/channels are extremely rare. I suppose its a good idea in theory, but not necessarily in practice.