APUG forgive me...
This may take some staging to re-create what originally was a planned, fortunate shot.
1 second exposure from above on a tripod, and just do it a bunch of times with people passing by. No big deal.
A fast walk (about 4 mph) is about 120 steps per minute; that means the right and left feet each move 60 times per minute. A slow walk would be about 30 times a minute. So a 1 second exposure sounds about right.
For a slow walk (2 miles per hour) the walkers head would move about 3 feet in 1 second
Keep the ideas flowing.. I'm looking for a suede jacket... And a volunteer from my neighborhood...
I'll try half, quarter, tenth. Looks like a brisk pace.