Many modern cars are completely drive-by-wire, and have a mode selector inbetween your controls and the car, which forces you into more fuel-efficient driving, e.g. ignoring if you push the speeder all the way down, and accelerating the car at an efficient pace instead. The more sensors and processing you get in a car, the better the car can be a this.

Other modern cars have an "eco display" or similar, which gamifies the experience. My previous car had some progress bars for different aspects, and I spent several boring commutes trying to get to a perfect 100%. (I did it once, I was so happy! Usually only got it to 98% before I hit the city and got stuck in traffic again)

Making automatics more efficient is a technological optimization problem. Making manuals more efficient is a human skill problem. I know which side I'd bet on in the long run. (Hint: Not the human)