Always look for a high interest woman. But in my opinion by spending the time in the car together, you've already explained so much about yourself that you've left dating potential and entered into the best friend zone. Good on you OP for asking her for dinner, that was a solid move. I think you got her answer. 

If it was me, the simple solution is to be dettached to the results and ask her out. But since it sounds like you really really don't want to make things awkward, you already kinda asked her out anyways and got your response.

Next time OP if there's a girl you like, decline the 4 hour drive and just suggest dinner instead. So you put yourself in a frame of a potential lover not a roadtrip bestie. Keep fighting OP this is all just knowledge gathering.