rotfl, that IS the Knight Bus xD And it isn't used in the theme park currently, it's in storage. It was used to get the stars on the night of the Grand Opening of the WWoHP (the one they only had private viewers)... It was an actual vehicle (although I believe it's really only meant for show, so :shrugs: ... Although I don't doubt they could pull off a Knight Bus, it's a transportation system for stranded witches or wizards. So muggles wouldn't really need it (we were allowed in Hogwarts as muggles, the Knight Bus is solely for witches/wizards. But other locations are open to possibility, because Hogwarts has already been "revealed to us")...
EDIT: Forget my first post, that IS the Knight Bus, but it's not the one they used for the park - it's Scholastic's book tour bus :/ lol...
Yes the one used for theWWoHP grand opening was an actual triple decker and looked more authentic. They had it sitting in CityWalk right after the opening but I have no clue where it is now. Probably in storage.