Sorry, this really grinds my gears ;)

> we know what the Overdrive gear in automatic-transmission cars means, and why you use it to pass a truck on the highway

That is not what overdrive is [1]. Overdrive is the very high gear that lets you nearly idle at highway speeds. Stepping on the gas would strain the engine, until the automatic downshifts, which is what the author seems to describe.

[1] http://www.wikiwand.com/en/Overdrive_(mechanics)

EDIT: it seems strange, coming from a miata driver, since those gearboxes definitely lack an overdrive, requiring high RPMs at highway speeds (like a racing transmission, tight ratios)