Identify a (Specific) Children's Book, Please!

A childhood friend and I are trying to find some identifying hints, clues, or information, for a children’s book. Please help! Here’s the description, to the best of our recollection:

a kids book written pre-1981 about a girl who lives in some future world where people don’t walk. everyone’s legs are bound into a small car-like thing that they travel around in. everyone lives aboard trains, and then they can drive their car things in and out of the train if they want to go somewhere. the girl “awakens” and somehow gets her legs dismounted out of her car-thing and then tries to walk. it was illustrated.