Yeah, that was my last car trip
When I was preggo with my first son, we drove seven hours each way to visit relatives. My legs swelled up to the size of a baby elephant :lol. This time (and actually, several times since that incident) we have taken the train to get where we needed to go. Riding the train figures out to be a shorter trip, when you add in the pee stops and dinner/switching drivers, etc. For us, a train is cheaper with two adults and 1 child than driving. Our car is really good on gas, but we always tend to buy more at restaurants/gas stations than we planned for. Of course, you can walk around as needed, and there are usually areas for kids to wander about (if nothing else, the snack car is a good place to stretch legs and play table games).
So, yeah, if that's an option, I would totally go for train :D.