Pile-ups on foggy motorways are often blamed on people driving too fast for the conditions. But according to researchers at the University of Wales, Cardiff, "motorway madness" may be due to an inbuilt inability to judge speed in the fog.
A team of psychologists, led by Robert Snowden, simulated the view from a vehicle moving along a road to show how perception changed in different conditions.
Tests showed that the subjects perceived the landscape to be moving more slowly in "misty" or "foggy" scenes than when the road was clear.
In another experiment, subjects were asked to "drive" a simulated vehicle at set speeds along a winding road.
They were found to speed up as conditions switched from "clear" to "misty" and "foggy".
Writing in the journal Nature, the researchers said: "Many horrendous vehicle accidents occur in foggy weather. Drivers know they should slow down because fog reduces visibility, but many still drive too quickly.
"The 'blame' for many such accidents may be due to a perceptual quirk; it appears that drivers think they are driving far more slowly than they actually are in foggy conditions, and therefore increase their speed."