Okay, I couldn't resist any longer - wasp nests as big as cars sound like
something out of the 'National Enquirer'.  Have they been contacted?  I'm
sure that the tabloids could come up with some sort of excellent headline with
this story.
 
Getting back to the topic - the various suggestions for getting rid of these
nests are interesting.  But are they approved uses for carbaryl?  (ie Is
carbaryl dust registered for use of pest wasps?)  The pop bottle suggestion
sounds like a good idea - BUT it is a rule of pesticide safety that one never
uses anything that could be mistaken as a food container for depensing or
storing pesticides!!!  Accidents do happen.