Here in Miami we have a free trolley (school bus size) system that extends along the greater downtown areas and some of the northern and southern suburbs. They are extremely clean and I VERY rarely see homeless on it (we have a rather large population too), I've been picked up at stops where homeless, also waiting (or trying to sleep), people didn't even attempt to get on board. In contrast, our free light rail system is full of homeless. they just ride all day 'cause its air conditioned and unmanned with few security patrols (they mainly utilize cameras on board and at stations). Perhaps this case maybe the solution is for a harsh rule system and driver enforcement, if they're too dirty/smelly don't let them on, and/or kick them off after X number of stops. I'm not sure what the policies are here, I base my assumptions on the way I've seen driver yell at patrons to pick up their trash etc. it seems like they actually care about the trolley.