From what I understand, the rear dual setup looked no different than brake lights (minus the 3rd light of course).

If you can see ONE bright light in traffic, in the fog, then you can obviously tell which side of the car is where. In other words, if you see a fog light but no car, then you know you're looking at the left side of the car, and the rest of it is on the right.

If you think of it, it's really slick. Just like navigation light combinations on boats depending on their propulsion, size, if they have a tow, etc., the one fog light setup lets you know EXACTLY what you are looking at.

Naturally the Americans picked up on the idea and stupidly dumped two fogs into some of the later product (Aurora for example). Most of the people I've seen driving them think it's a light show, and drive with them on all the time.
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1992 940 wagon, low miles
as well as others.