So that's what carts are for? Fascinating!
These cars are owned by the Brooklyn Historic Railway Association, an organization run by Bob Diamond (of Atlantic Avenue Tunnel fame) that hopes to re-establish trolley service in Brooklyn. They've struggled for more than a decade to obtain city approval for the project, and at one point were even laying tracks in the street, but all that now remains of their efforts are these three rusting trolley cars sitting behind the Fairway supermarket in Red Hook.
Manhattan's 34th Street Partnership BID may have outgrown these dinged-up old planters, but Red Hook isn't too proud to put them to good use. You can find quite a few of them livening up the waterfront around here.