Neal Stephenson's Anathem. I have several more audio books ready for the next few phases of my sojourn but for now I give Anathem a big thumbs up.
Audio books tend to shorten the driving experience if they engage you at the level you want, need or desire. For me that means a solid storyline that meanders a bit. Short, fast and direct is not what the long road provides, so the stories need to avoid brevity as well. Trust me when I say 28 CDs is not short. I do take breaks for music and once in awhile some crazy ass right-wing radio commentary. But mostly I go with the audio books.
Anathem is science fiction set on another world, which strangely resembles earth. The characters as a whole have the same social and political failings as do we earthlings but Stephenson knows how to tell a tale. All of the side stories keep you moving towards the big finish but nary a once does the true nature of that finish get revealed. Hints, yes. Distractions, plenty.
A great listen for a lengthy road trip.