ABSTRACT
The main meteorological hazards which confront road users are ice, snow, wind and fog. These are exacerbated whenever they occur in combination and in darkness. Ice and snow can cause as much disruption as fog, but they can be predicted with a fair degree of certainty, they can be monitored in situ, and can be cleared or ameliorated by gritting and by the use of snow-ploughs. Wind conditions are usually forecast accurately, and the hazard can be reduced locally by the careful design of road sections and bridge structures, and by the use of wind-breaks. Fog is the least predictable of these hazards, both in terms of its variability over time and from place to place. It is expensive to monitor visibility in real time beside a motorway. There is no known means of preventing the occurrence of fog, or of dispersing it at an acceptable cost once it has formed. Fog can persist in some localities for many hours at a time.
