I picked the "am lost in thought..." option, which is closest to what actually happens; but really it's somewhere between that and "no", because it really happens very seldom.
When I'm in severe overload, right on the brink of meltdown and probably left with just single words to communicate with, I have some problems with awareness of the world around me. Not necessarily being unaware; it's just that I don't really have enough brain left to think about what all the things around me mean. At this point, it is possible for me to walk into traffic without thinking about the fact that I am walking onto a road; or just keep walking on the same path without noticing there's something in front of me. It feels a little like the world is "far away" or irrelevant.
Oddly enough, though, it's a very narrow range that actually puts me in danger of walking into traffic, because with only a very little more, I am overloaded enough that I am having a difficult time standing up because keeping my balance also takes some small amount of concentration, and am likely to just sit down wherever I happen to be until I can get my bearings again.
I have walked into things (and on occasion run into stationary objects on my bicycle) because I was too overloaded to think about where I was going, but not lately, not during the past year or so. When I had a car, I would always do a mental check before I left to make sure that I was able to drive safely; if there was any chance I couldn't, I would just stay home. (I ought to do that with my bike, too, come to think of it.)
So yeah, it's pretty much a problem I've learned to deal with--I just don't get anywhere near a road (or other dangerous place) when I know I'm getting near a state where it'll be unsafe for me. Any meltdown I can't stave off that way usually happens too fast for me to balance on the dangerous thin edge between "able to remember to avoid cars" and "able to walk into the road".