I just realized something with the distance fog option in LFS.
Indeed, it doesn't add a fog like the usual distance fog you'd see in FPS' or other racing games.
Rather, it adds a filter of less contrast on the background textures (mountains etc).
Which gave me the idea of something that would work like this :
0m______________________/_ _ _\ _ _ _ _ _200m
between 0m and / you'd see normally, with what you usually see when driving (Contrast = 1). Between / and \, it would be the "limit of sight" zone, in which the contrast of the textures that would appear between the two distance marks will be varying linearly between 1 and 0 (0<Contrast<1). Between the \ and the 200m mark, you'd see only grey for all the textures (contrast = 0).
Choosing between Light and heavy fog would determine the width and the position of the /\ zone (light equal longer and further from the mark 0m and heavy means closer to mark 0m and less large). The color of the fog would be determined by the weather you chose (clear day = light grey fog / cloudy afternoon = darker fog).
Do you think it is possible ?