Ian wrote:
The problem with fog lights, both front and rear, is that few drivers appear able to judge 100m and hence know when to turn them on or off as appropriate. I am not saying that a few m over the 100 is a bad thing and so leave them on but a little more thought from some would be appreciated.
Exactly the point I was planning to make!
Additionally, once you are established in the middle of a queue of traffic, what is the advantage of having your rear fogs on? The driver behind knows you are there, and can see you at a 3ish second gap with your tail lights alone, even in pretty dense fog; you are all travelling approximately the same speed. Driving in the patchy fog today, I had drivers ahead of me in a queue of traffic actually turning their fogs on at the first hint of thickening fog (vis still well over 100m), did they genuinely think I was going to lose sight of them?!
Another effect I observed, as I progressed to the west and the fog thinned and pretty much disappeared, was that when drivers leave their rear fogs on in the dark, in addition to rear dazzle, it can cause errors of perspective with your observation. As I believe I mentioned before, monocular cues, such as brightness of lights and colour, are used by the eyes/brain to judge distances once you pass about 6m away from the eyes. Having both bright/vivid and less bright/vivid lights on the same plane at the rear of the car can make them appear to be at different distances from the eye. This phenomenon manifested itself to me as I was passing a queue of traffic, on the two-lane M54, rounding a gentle bend to the right. The right-hand lane immediately ahead of me was clear, but looking some 200m or so ahead into the bend I was unable to tell for sure if there were any vehicles in it, due to approximately half a dozen drivers still having their fogs on in the gin-clear night. I have visual accuity in excess of 20/20, am not night or colour impared and was not fatigued or under the influence.
When I was stationed at Leuchars in Scotland I remember seeing some of the overhead gantry signs on the motorways broadcasting such wisdom as 'Be a considerate driver'. I am sure at some point I saw something along the lines of 'Avoid rear dazzle - limit fog light use'. Words to that effect could be usefully employed in foggy conditions where overhead gantries are fitted, but the wording would have to be carefully chosen to discourage inappropriate useage, but not legitimate use. Can anyone think of something that gets the message across and would fit on a gantry sign (approx 20 chars by 3 lines)?