I did most of the pre retrofit sampling for the west side of the bridge (I’ve done probably the majority of it for the bay area freeways).
That involved a lot of trekking around beneath all the structures. When I was a noob out here, that stuff was quite the eye opener. I had literally seen areas with garbage 3 feet deep, with rats drinking from puddles in broad daylight, in which a human form rose from beneath the sea of garbage and shambled off.
You don’t lean against freeway columns in the city, people back up against them to take a dump and splatter them. I saw one area which stayed dry with a surface of fine dust the consistency of talcum powder. The rat tracks in that dust were so thick there were no clear patches in it, they all overlapped, for an area of over an acre. When the sun went down that place must have looked like a scene from Ben.
Some of the homeless are nasty mean, and others are STARK raving lunatics. I saw people who could, I s*** you not, be a walk on cast member of the walking dead without makeup...
You run into the occasional one that seems sane, but just decided to drop out of functional society. I could never for the life of me figure out why they just didn’t go live off the countryside or hermit up in the hills, I myself would live in just about any environment except a city if I were destitute.
Familiarity, perhaps, but also there's an abundance of shelter in the city. I believe there was, at some time a few years ago, an entire complex, or "hive" of homeless people ensconced in the NYC subway tunnels. IIRC, the matter became a public scandal and they were flushed out.
Back in the day, I used to take a bus out of the Port Authority Terminal on the West Side to go back up to college. One time, as we left the terminal, I observed some cops standing over an inert form across the Avenue there. No flashing lights. A five second episode of THE NAKED CITY.