No one can walk anymore.  They only drive in large wheeled homes and mobile offices.  They even have motorized vehicles in individual sizes for transporting themselves outside of these wheeled homes.

Everything has been paved over with roads, except a small area with a flower or a tree in it.

Fascinated by this unpaved area, the girl wheels over to it only to find her wheeled individual vehicle can’t go on the unpaved area.  She is forced to get out of the vehicle and make her way across the green space without motorized assistance.