This falls into the category of "things I should probably be embarrassed about not knowing."
Comments in a recent post
on the blue made it clear to me that (1) people have strong opinions on the subject of passing on the right and (2) I have no idea what that actually means.
As a coastal, urban, U.S. resident who drives very rarely, and even more rarely on roads that aren't either deserted or six lanes wide, I've never given any thought to the idea of "passing on the right." When it came up in DMV tests when I was in high-school, I always assumed it was some archaic convention that meant something when applied to roads in some distant place and had nothing to do with me.
Some time with search engines has failed to enlighten me. Like the metafilter discussion, I gather only that people who know what it means seem to care about it, and can't find a clear description of what it is they're talking about.
The California DMV claims that passing on the right is legal "Upon a highway within a business or residence district with unobstructed pavement of sufficient width for two or more lines of moving vehicles in the direction of travel." That more or less describes every road on which I've ever considered passing anyone on either side for any reason.
So, please, educate me. What does "passing on the right" actually mean in the real world? Is it something that only applies to one-lane highways in the outback, where passing on the right seems not only dangerous but downright crazy? If I'm on a multi-lane highway and am traveling faster than someone in a lane to my left, does that count as passing on the right? Is that bad? (If so, it seems utterly inconceivable that one could avoid doing this. The US highways are stacked with slow-moving, left-lane drivers.) If I'm behind someone in the left lane and move right lane in order to speed up, does that count?