I don't think cars are ever going away, even if public is the main transportation method. Which obviously sucks, but it's the way it is.

I've always imagined a protocol that lets cars communicate their planned speed. I'm pretty sure this is how cars will work in the future. A decentralized mesh of coordinated vehicles. This means that cars can:

• Maximize constant speed time, improving energy consumption and traffic flow.
• Minimize distance between vehicles based on speed and acxeleration while complying with safety standards.
• Connect to devices such as semaphores in order to tell if the vehicle will pass or not, to make a better decision.
• Connect to other mesh devices such as AI cameras that feed events to the vehicle mesh.

Public is obviously the best option though. Imagine a city with no streets, only subterranean public transportation. You wouldn't even need such a large public transportation system, cities would be a fraction of the current size. I wonder what percentage of the area of a city is wasted on streets.