You can further optimize the setup by not installing engines/motors in all of them. So maybe you have one car providing locomotion, with the rest following behind and designed for carrying.
If we do all of that, then we won't need to train them to know how to operate in traffic. Perhaps we can give them a name in honour of that fact?
And all the power could just come from a few large centralized facilities that are super efficient. We could just use thin strands of metal to get it to the vehicles over head…