The experiment studied how fog affects traffic on the M4 motorway. Day and night-time fogs were tested separately. In day-time fogs with visibility down to 150 meters, traffic speed remains stable until visibility drops below 200 meters. Night-time fog shows more variable speeds but follows a similar trend. When visibility is above 150 meters, most drivers can stop in time, but lower visibility leads to slower speeds and closer following, increasing the risk of accidents. About one-third of vehicles follow too closely in foggy conditions.