The fog on a China highway was so dense that drivers had a big problem with visibility. The result was that a mass accident was noted, Although a driver tried to warn vehicles coming at speed. Fog is one of the most dangerous weather conditions on the road, Especially on highways where people drive at greater speed. Significantly reduces visibility and can cause chain accidents. The observance of security rules, Caution and timely lighting on fog lights can help avoid accidents. In case of very dense fog, It is best to stop in a safe place and wait for conditions to improve.