Avoiding and trying to predict the paths of other people while walking is a challenge for me, too.
I use a cane when outside of my home, and this generally serves as a notice to others that I am a person who has "walking issues".
Still need to be alert to the hurried walker, the cell-phone-chatting walker, the kids-on-both-arms walker, the arm-in-arm lovey-dovey walkers, the dog-walker, other "challenged" walkers, and the "I just learned to walk" walker! I try to choose my walking times and paths very carefully. But it is not always easy.
p.s. I too, was able to walk miles at a time. Now, I am grateful for the short amounts of time I am able walk. Always on the look-out for a place to sit! (Just in case.......)