I'm trying to remember the title of a book that deals with a group of people that travel to different worlds in a car or a car is involved somewhere in it. I thought it might have been a Robert Heinlein book but I may be wrong. Any help would be appreciated (it's not Job: a Comedy of Justice). Thanks!

One series along those lines is the Skyway series by John DeChancie. It starts with Starrigger, followed by Red Limit Freeway and Paradox Alley.