The frequency and duration of thick fog (visibility less than 200 meters) in Great Britain has been analyzed for the period 1958-67. The highest mean annual number of days with thick fog at recording sites was 17 at 0900 Greenwich Mean Time at Watnall (Nottinghamshire). Generally, thick fog was found to be relatively infrequent, patchy, rarely widespread, and of short duration. Its frequency inland has been falling in recent years, probably because of the clean air act, 1956. Four thick fogs of twenty-four hour duration on weekdays reduced traffic flow by about 20 per cent. (previous reports had indicated considerably greater reductions at weekends). The numbers of fatal and serious accidents and casualties were reduced, but slight accidents and casualties increased significantly. Accidents in darkness and those involving pedestrians were reduced significantlly, whereas those involving more than two vehicles were increased significantly. Overall, there was no change in the fatal and serious accident rate per unit of traffic, whereas the slight injury and total accident rates increased by about 70 and 50 percent, respectively. (Author/publisher)
Samenvatting