Why does fuel economy get better on the highway, but EV range gets worse?
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Engines are more efficient at a specific RPM and power output. Cars, between the engine and gearing, are generally tuned to around 50-70mph being the most efficient as that is the typical speed they are driven at that can easily fall into the typical efficient ranges.
That is countered by higher speeds needing more energy to maintain. This is primarily due to wind resistance – doubling speed quadruples the drag – though other friction losses can play a large part as well.
Electric motors don’t have that initial behavior, but do still have to deal with the increasing energy requirements. This means that going faster with an electric system is basically always less efficient, though there is some exception at very low speeds – less than 10mph or so. Electric vehicles also include regenerative breaking, which helps a lot with stop and go movements as well as on downhill roads.
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