Could you elaborate, just curious what you mean. they have a lot of police activity or they just chat a lot?
They are just that busy and very active. I generally don't listen to police talkgroups (on any system). I currently listen mostly for determining scanner performance, etc. on a Phase 2 system and the level of activity on these talkgroups makes that easy - they are nearly always active.
MdTA and MSP Highway are the busiest talkgroups on the system at this point. In fact if you can hear and listen to 4 talkgroups (Tunnel, Port, MSP Highway, and Hatem), they are so active (working) you may not hear much of anything else on this system. You really don't think about how much traffic flows up and down I-95 from Delaware to Howard County until you hear these 3-4 talkgroups and them it becomes obvious. MdTA Bay Bridge, Maryland Capital Police, Corrections and other police organizations are becoming more active all the time. Dundalk Marine terminals, MDE, etc also - and there's a fair amount of full time encrypted talkgroups as well.