On the way to and from work, part of my journey is on a sidewalk on which the street is to one side, along with inconveniently placed trees right in the sidewalk, and a couple-inch ledge that leads to a fifteen-foot tumble down a hill on the other. My Segway is about as wide as a wheelchair, so while there's little room to maneuver, it's not difficult to keep from hitting the tree or falling off the edge of the sidewalk; I've never fallen off the side, and only come close to a tree a couple times.
But for the past week or so, things were different. The leaves have begun to fall here, and suddenly one cannot tell by looking whether they're half a foot into the safe zone or half an inch away from a very uncomfortable situation. The following diagram makes it seem as if you can just barely make out the edge of the sidewalk, but let me assure you that with an inch-thick carpet of leaves, this is quite impossible, even in daylight.
I'm almost surprised that I didn't slip off at some point. I was going to take a picture to better illustrate how impossible it is to tell where you're going through a thick carpet like that, but it seems that they cleared the sidewalks of leaves just this afternoon.