fog and road traffic

thick fog occurs in great britain on about 10 days each year: it impedes traffic and some dramatic accidents occur on high speed roads. overall some two per cent of all road casualties occur in foggy weather. although the total number of motorway fog accidents is small, accidents per kilometre are more numerous than on other roads and more serious. the physics of fog and the prospects of reducing the number of fog accidents by fog dispersal, better warning, improved lighting and the use of electromagnetic and acoustic radar are discussed. current valuations of accident costs are used to estimate the additional expenditure on vehicles and roads that might be justified assuming that it resulted in a halving of fog accidents. it is probable that the most worthwhile countermeasures to fog accidents may be found in systems of traffic control that have a wider application than only in fog. (a)