80s Sci-Fi / Horror / Road Trip about Time Lines disintegrating, traveling in a Motor Home

'80s sci-fi book. A father either rents / buys a Winnebago for a road trip his family really doesn't want to go on. There's tension with his teenage daughter, and I think there was a younger son. As they're traveling, they somehow end up getting pulled over and have to follow the police back to what turns out to be hell. The cars they pass along the way contain screaming people, and when they get there, hell is a bureaucratic nightmare. They eventually escape and somehow discovered that the strands of time / reality are unraveling. There's something about a world where everyone has to speak the truth all the time, and they almost get into it with a waitress who can't hold back her opinions. I remember it being very clever and amusing, but not the title. Thoughts??

This might be To the Vanishing Point by Alan Dean Foster.

This sounds crazy. I'm totally going to read it.

I'm with >3 weener:. If you find the title please post it.

OH MY GOD, that's totally the cover. Hailelib, you have NO IDEA what a mystery you just solved for me. Thank you sooooooooooo much!!!!!!

You're welcome.

Thank you - one more to add to the reading list.