Yes.

And it's a good thing to keep in mind with talk about self driving cars and 100mph HOV lanes on HN recently.

But you don't need the lanes to go 100mph - during the morning traffic jams, they could just go 100kph (or ~60mph), taking a tenth the time and half the normal fuel consumption of a commute.

Once that happens, you can be damn sure that every new car purchase by someone that commutes will have the system.

So while you may be right that 100mph lanes aren't a good idea, the idea has a lot of merit.

With self-driving cars you can safely keep traffic bumper-to-bumper which reduces aerodynamic drag significantly. Self-driving 100mph HOV lanes could very easily be more efficient than human-driven 70mph lanes.

I dunno, actually. Given that cruising is very efficient compared to stopping and starting, I think if you decided to optimize for fuel economy at exactly 100mph you could probably squeeze that kind of fuel economy out of a car. Optimize for aerodynamics, give it a tiny cross section (I'm thinking passenger behind driver), lowest rolling resistance tires you can manage, and put in a small engine and a super-long gearbox so that your engine is turning at maximimal efficiency when the car's doing 100mph. I don't think it'd be that difficult. On the downside it would of course be tiny and have terrible acceleration.

Or, to put it another way, my big heavy car gets nearly 30mpg when cruising at 100mph, so all you really gotta do is reduce drag.