EVs can achieve 90% efficiency in the real world. ICE top out at about 35%. For EVs, how you achieve maximum efficiency is very different than for ICE. With an EV, there are two primary loss areas, friction and aerodynamics. At low speeds EV efficiency suffers because friction is higher, but that drops away by about 25 mph. Aerodynamics builds as you go faster. The efficiency sweet spot for an EV is around 25 mph and there is nothing you can do about it. That's why the hypermiler records are all set at driving around 25 mph for 24 hours.
ICE are vastly more complex, but they get their best efficiency when running constantly at the sweet spot RPM. Hybrid cars attempt to squeeze as much as they can out of the ICE by running it at or close to that sweet spot all the time and augmenting what the engine puts out with batteries.
ICE have a narrow band of RPM where they can run without either stalling or ripping themselves apart, which is why you need a transmission. A single gear transmission on an ICE that wouldn't stall starting from a stop would rip the engine apart by about 20 mph. ICE have been getting more and more gears in recent years and even CVT transmissions in an attempt to keep the engine RPM as close to the most efficient spot as possible at as many speeds as possible.
With say a 3 speed transmission, the car won't kill itself driving 35 mph in 3rd gear, but it won't be turning over at the optimum RPM to get the best gas mileage. Most ICE are geared to get the best RPM for gas mileage around 60 mph, so their efficiency usually peaks around there when you're driving constant speed. Some ICE also have other features that help improve gas mileage on the highway like shutting down cylinders when not needed. Cadillac did it first in the late 1980s, but they discontinued the engine because there were few mechanics who could work on them, but the engine design has made a comeback and a lot of GM cars with larger engines disable pairs of cylinders on the highway. I don't know if they do it with the V-6 engines, but they do with the V-8s. They go down to 6 then 4 cylinders on the highway.
ICE still take an aerodynamic hit at highway speeds, the same Physics works on them too, but because they are so inefficient to start with, you don't tend to notice is as much. Think of it as an average grade in a class in school. If you're average near the end of term is 90%, a 30% on the final is going to kill your average. On the other hand if your average is 35%, the 30% isn't going to change your average much.
ICE get such horrible efficiency overall that one more inefficiency doesn't dramatically reduce the average much. Because EVs are so efficient, every little thing kills the average efficiency.
A gallon of gasoline has 33.7 KWH of energy in it. Diesel is in the same ballpark. If you get 30 mpg, that's 1123 Wh/Mi. The Model X, which is one of the least efficient EVs averages better than 3 times that. The only reason EVs are running rings around ICE for range is the best batteries we have for cars today are only about 1/33 the energy density per gallon of space as gasoline.
Fossil fuels are the dominant transportation fuel today because of their energy density, but they lose a staggering amount of that energy making heat when burned.
