Now you've got me concerned about a potential design issue.
When a subway with a third rail throws a shoe, no biggie -- everything's (sub)ground level.
When an elevated monorail throws a shoe, now you've got a flying debris issue. Admittedly, exposure to guests from the monorail crossing their paths is low, but there are several such points, and as the photo showed, timing becomes an important consideration. -- as in not being under a monorail when a shoe could come flying off.
I will now go and reconsider my life vis-a-vis walking, driving or standing under monorail beams.