This study defines fog as an aerosol consisting primarily of water droplets. The main effect on road traffic is the contrast reduction as a result of the scatter of light in the aerosol. Absorption plays only a small role. The effect of the contrast reduction is that many objects in the field of view, that are very easily visible in a clear atmosphere, cannot be seen properly, and often not at all, during fog. It appears that fog is a considerable traffic safety hazard on all roads, particularly on motorways. The study also discusses how far road lighting can help to reduce the accident risks that arise in fog on motorways. Road lighting appears to be an effective road safety measure on motorways. The benefits are especially in fog. It is recommended to install general purpose lighting systems on motorways, particularly in fog-prone regions. It is also recommended to apply length-wise mounted catenary lighting systems equipped with low-pressure sodium lamps for general purpose lighting for motorways in fog-prone areas. The study is based on a paper presented at Japan Highway Corporation, Tokyo, 12 July 1990.
Abstract