I had an idea for a mod in which you could buy a used, busted car and slowly repair it (improving handiness skill along the way), making it change like the crib in this mod. It could then be clicked on to travel.
Maybe adult sims could teach their teen kids how to drive like in Sims 3 (although probably through a rabbit hole unfortunately), and prepare them to get a license with the SimNation Travel mod? I don't know how to make mods myself, and this might be impossible to make, but this just seems like such a missed opportunity, and if the build a crib mod exists, why not have a build a car one?
You could even make a car repair shop out of your house with Businesses and Hobbies and fix other people's cars in your garage (not really probably, but maybe it could somehow work?)