[CRConrad]

> Aren't ICE cars often more efficient at highway speeds?

No. They're more efficient at constant speeds, because the ICE can only be really optimised for a very narrow RPM band, but that need not necessarily translate into higher speeds.

Just choose a lower gear, and watch your fuel consumption drop significantly below what it would be at higher speed in a higher gear.

The main reason for this is that air resistance, which costs energy (=fuel) to overcome, rises not linearly with rising speed, but in proportion to the square thereof.