Don't Make Yourself Comfortable

The tram I was on this morning had four of these things:

Six seats have been removed to make room for each of them. That's 24 seats gone. Can you think of a reason?

These things (some people call them "bum racks", but Yarra Trams calls them "bum-rests") take up a lot of room, so aren't really adding much standing room. On my trip I saw a maximum of two people at a time using each one - one person between each of the vertical bars. Granted that wasn't in peak hour, but when the tram is packed, could more than six people fit into the area that originally held six seats? Maybe, if the bum racks were flatter and didn't intrude into the passenger area so far, but they stick out more than half the distance of the original seats.