A scorcher killed a lady-ped here in Rochester, NY on the MUP some years ago. He was tooling along and overtook a couple of walkers from behind (without calling out), and one of them coincidentally turned aside just as he came up behind her and WHAMMO! Most folks out there have been more careful since then, but I've noticed that the guys with the most expensive kits never call out when overtaking someone....too busy making time to speak to us Proles. I doubt that speed limits will do much to diminish that kind of stupidity. Biking-Folks have to attend to the fact that the trails are often populated by kids, older people, dogs, chatty groups of walkers, the I-pod deaf, horses, etc and should ride accordingly. It's not as though such hazards are invisible.