Most road trips I'm in the low 30's.
However when I traveled down south the first summer I had the car I drove around on gas they had that doesn't contain the winter blend crap Ohio has, I got an amazing 40mpg, it's only happened once.

Using cruise and running 70mph and drafting off of semi's should result in a high 30's average for freeway running. But you need to really pay attention, chasing Z's in the triples isn't doing you any help.