Driver behaviour in fog is not only a question of degraded visibility - A simulator study

Driver behaviour in fog is not only a question of degraded visibility - A simulator study: The aim of this simulator study was to determine whether the effects of fog on driver behaviour were identical for a given road type and whether they could explain fog-related crashes according to road type. Thirty-three participants drove on both two-lane rural roads and motorways according to three visibility conditions (clear weather, 60 m-visibility and 30 m-visibility) and two driving situations (non-free driving and free driving). The variables were: Speeds (Ss), Headway Distances (HDs) and Headway Times (HTs). Fog was simulated using special software designed as part of the French Predit project VOIR, allowing both realistic vehicle headlights and halos to be displayed. The results showed that the drivers decreased their speed with decreasing visibility distance, i.e., speeds were slower in the 30 m-visibility conditions than in clear conditions; but, speeds on the two-lane motorway remained faster than on the two-lane rural road, even for the denser fog. In the 30 m-visibility condition, the faster speeds driven on motorways than on two-lane rural sections violated those advocated by the French Highway Code. The distances travelled in conjunction with the speeds driven according to the two-second rule revealed that HTs less than 2 s and small HDs do not necessarily match with hazardous driving.