There are regular 100+ car pileups in the central California valley due to fog. Cars crash in a lot of situations because the driver simply can't see. We need something better than vision to avoid these kinds of accidents.

Coordinated cars won't work unless all cars are built the same and all maintained 100% the same and regularly inspected. You can't have a car driving 2 inches from the car in front, if it can't stop just as fast as the car in front. People already neglect their cars, change brake compounds, and get stuck purchasing low quality brake parts due to lack of availability of good components.

Next time you see some total beater driving down the road, imagine that car 2 inches off your rear bumper, not even a computer can make up for poor maintenance. Imagine that 8000lb pickup with it's cheap oversized tires right in your rearview mirror with it's headlights in your face. It's not going to be able to stop either.