Rest Areas Safe?

Well I've been all over the country. Some states have beautiful rest stops with 24hr security and free coffee. Some have 55 gal barrels for trash and nothing else. I never overnight, but I frequently take a short nap during a long day. mostly in the day. At night I prefer a nice campground with clean bath rooms and showers. Once I was parked at a rest stop on 495 outside the Boston area. In the middle of the day a pimp pulled up and 4 "working" girls got out and started going from truck to truck selling Girl Scout cookies maybe? Broad daylight! Now way out in the middle of the dead flat great plains, I've stopped at rest areas and hardly seen another soul for hours. I just assume 99% of folks are allright, but that 1% can show up anywhere.