In one experiment, nearly 200 participants boarded a double-decker bus for a tour of Philadelphia.

One such patient is Eric Decker who had had bariatric surgery at Cincinnati Children's four years ago when he was 17 years old.

The company's 164 trams, including two open-balcony trams for tourists and private hire and one special maintenance tram, make up the world's only fully double-decker tram fleet.