Why does fuel economy get better on the highway, but EV range gets worse?
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Hybrid range gets worse too.
There’s a balance between two principles here:
1. Pure gasoline (ICE) cars are incredibly inefficient in start-stop traffic.
2. Driving fast uses a lot more energy than driving slow (air resistance increases with the square of the velocity).
When driving in a city point 1 above applies, but not point 2. Hybrids and EVs have a clear advantage here since they can make use of electric motor torque and regenerative braking.
On a highway there is no or very little stopping, so regenerative braking and low-speed torque are of no advantage, only slightly beneficial when going over hills. So point 2 kicks in and the efficiency comes down to aerodynamics. The ICE cars will be running at or near their boilerplate efficiency without start-stop traffic impeding them. The EV will still be several times more efficient than the ICE because of basic thermodynamics, but the efficiency of all vehicles will be reduced by traveling at higher speeds. This is why you sometimes see EV drivers “hypermiling” in the slow lane at maybe 20% below the speed limit.
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