In 1960, British architect Geoffrey Alan Jellicoe proposed the city of the future for suburban London. Motopia was to be a residential town with all roadways elevated to the tops of the buildings. The ground was to be reserved for pedestrians -with moving sidewalks. He even had plans to insulate the overhead roadways to stifle traffic noise!
Planned for construction about 17 miles west of London with an estimated cost of about $170 million, Motopia was a bold—if somewhat impractical plan—for a city built from the ground up. The town was envisioned as being able to have a population of 30,000, all living in a grid-pattern of buildings with an expanse of rooftop motorways in the sky. There would be schools, shops, restaurants, churches and theaters all resting on a total footprint of about 1,000 acres.
The biggest draw of the plan was that people never had to worry about being hit by a car. However, we all know that some drivers don't stay on the roadway, and being squashed by a falling car is even more terrifying than being hit by one. Motopia was never built, but you can read more about what could have been at Paleofuture. Link