[quote=spdrun]Cars with 6, 7 speed transmissions or CVTs already have a tall top gear at detriment to throttle response. The issue isn’t gearing at this point — efficiency is limited by air, drivetrain, and road drag.

You might be able to gain efficiency by making cars lighter (lesser crash safety if they crash less), but above 80 mph, drag is mostly from air resistance. Frontal area isn’t going to change much unless you start building 4-person autonomous motorbikes.

And if anything, autonomous cars will be even more bloated since people will want to stand up, eat, go to the toilet. Think of an 80s VW Microbus except scaled up 25% in all directions for fatties.[/quote]
Average cars today still have drag co-efficient between .25-.35. They can totally reduce that to the high teens low 20s. Think Model 3. Regarding drive train, it’s not about the amount of gear but about the gear ratio of the overdrive gear. Then there’s the tuning of the engine. Think gas throttle response vs diesel gas mileage. If we no longer care about throttle response, then we can come up with engines like the turbo diesel that get awesome highway gas mileage at the detriment of throttle response.

Also keep in mind we’re talking about varying degrees of efficiency, not absolute in-efficiency. I would take slightly less efficiency for the convenience of autonomous car over train any day of the week and on Sunday.