This article examines the relationship between road lighting and road accidents, and reviews some of the relevant literature including studies by the International Illumination Commission (CIE). About half of the road accidents in industrialised countries are at night, even though night-time traffic flow is only about 20-35% of total traffic flow. Night-time accidents also tend to be more severe. The CIE draft report has examined and analysed 63 studies from world-wide sources, which have two main types: (1) surveys of existing lighting and accident rates; (2) before-and-after studies, attempting to correlate a change in accident rate with a change in lighting. Very few of the studies cited by the CIE are statistically robust, due to the expense and difficulty of performing them. The installation of lighting is usually found to reduce accidents, but studies usually give little indication about the effects of quality and quantity of lighting. Measures of visibility include: (1) revealing power; (2) visibility index (VI); (3) visibility level (VL). There is at present strong resistance to basing national and international codes of practice on them, because of the complexity of driving at night and because of lack of field validation. However, these measures can be developed further, so that modified forms of them might later be adopted as standards.
Abstract