M.H.
We just got back from a 6 hour road trip with our boys. Both boys (2 1/2 and 15 months) are still rear facing and I wouldn't turn them around for a long road trip. The risk of internal decapitation seems a bit greater to me if an accident happened going 75pmh than if were just in town going 40mph. We just kept lots of books and cars in the diaper bag that I could easily get to and hand them off if someone got bored. We also took sippy cups with water and stopped a couple of times so they could get out and run around to burn off some energy and boredom.