amused
There were six of these in total (two were behind the four you can see here). I wasn't sure what these were for, but the coating of playa dust gave a hint.
As I walked back from the post office, the fleet, now back under way, passed me heading east on Main Street, and I could see (but was not quick enough to photograph) the Black Rock City Transit sign on the buses. I speculate that the drivers had parked where they did so they could go have lunch.