The velomobile (electric or manual) is the most efficient transport in energy per mile. You could easily design something like a self driving podbike, maybe a little bigger, weighing maybe 100kg.

And self driving also allows for new configurations, e.g. two seats that face each other because you don't need a steering wheel. That means much more narrow and aerodynamic "micro cars" that could solve a lot of edge cases for people who can't drive or not that long or fast (50kmh / 30mph). They might compete with a big bus.