[Publius6961]

Such a car would in fact use no energy except in the first few seconds when it was accelerating up to speed. After that it would just coast.

You should have stayed awake more often in high school physics class.

Air resistance and drag goes away when you're going a constant speed?
On what planet?

[HangnJudge]

Assumption stated in reply

He was assuming a frictionless vehicle, part of ongoing discussion of energy expenditure from acceleration vs steady state parasitic loses

[Yardstick]

Publius, you ignorant slut.

It's common to make reasonable simplifications in these kinds of back-of-the-envelope calculations. In this case omitting air resistance is reasonable since at 20 km/hr (which is what, 12 mph?) wind resistance would be small.

My main point was that you can't use a unit that expresses energy used for a given acceleration as though it were energy used for a given distance travelled. That's mixing apples and oranges.

A further criticism would be to point out that most driving that occurs at 20 km/hr is city driving and involves lots of speeding up and slowing down. When you account for those accelerations, you're going to see a lot more energy used.