As already pointed out in the article, losing BOTH shoes (if not attached together) at the same time and place is not likely to begin with.
If you throw a pair of shoes out of a fast moving car, they won’t tumble uniformly, and they’re not likely to remain together, and even if both stop on the highway a short distance from each other, they won’t both remain together on the highway for long before one gets kicked up by a wheel and sent flying.
If you throw the shoes out the window one at a time, and it takes even a few seconds to collect the second shoe, they will be pretty far apart, and still no guarantee they’ll both remain in sight of motorists, on the road.
A few likely places for mates of shoes, if still near each other:
- In the weeds, off the road
- In a nearby storm drain
- Under other trash
- Kicked up over the median (opposite side of the road)
- Cleaned up from the from the shoulder by ‘adopt a highway’ or road maintenance, while the median is left for another crew.
- Kicked up, jammed in an undercarriage or landed in the bed of a pickup and ‘randomly’ deposited somewhere else, even in another state.
Small samples plays a role in this as well. You might well find a shoe’s mate if you searched a quarter mile in each direction from the shoe, on and off the highway. Of course there’s no guarantee the other shoe will be around. Few people would bother to perform an exhaustive search for a missing mate of one shoe discovered on a highway. They see a few instances of ‘one shoe’ and it’s a phenomena. Like the media calling every incident involving buses a ‘plunge’, therefore ‘Bus Plunge’.
If a pair of shoes are together, a whole class of people might be very likely to pick the pair up. Only someone desperate (or one legged, or odd) would pick up a single shoe.
A better experiment would be to actually plant and/or throw pairs of shoes out a car window, and then monitor what happens to them with a camera. This is technically ‘littering’, so go to a state like Florida that doesn’t seem to mind garbage being strewn all over their highways. If scientific enough, it might be worth an ‘ignobel prize’.
Tag them and track where they end up. Compare the fates of different kinds of shoes.