>I've seen sliding side doors on late-model buses, dual side doors on 
     >microbuses, but what does the term barndoor term refer to?
     
     Barndoor is the name given to early (pre '55 buses - I think) buses, 
     because the engine lid was huge, like twice the height of a late model 
     engine lid. This also meant that the 'barnoor' buses didn't have 
     opening tailgates. The back window/panel was fixed.
     
     Opening the 'barndoor' reveals the engine bay with a shelf over the 
     top that stores the spare wheel lay down.
     
     Since this age of bus has become known as the 'barndoor' bus you can 
     actually get a 'barndoor' pickup - now that's a bit confusing...
     
     Lee.