This work set out to improve the basis on which the cost-benefit of installing and operating street lighting on local authority managed roads of all types is calculated. To do this it is necessary to derive factors, by which lighting will reduce the number of accidents, on a range of road types. Such factors are used to calculate cost savings due to an expected reduction in accidents.
The project analysed existing accident data and obtained, collated and analysed new data from local authority and other databases to permit improved predictions by providing accident reduction factors for different categories of road and lighting levels.
A lack of data on other variables that affect accidents, than those collected, became apparent. As a result, these could not be properly accounted for in the statistical modelling. The work demonstrates that such studies, however large, are dominated by the lack of independence between the presence of street lighting and the potential accident rate, which heavily obscures the effect of lighting on accident rate. This is thought to be because the majority of sites which can benefit from street lighting already have it installed. The inability to show a benefit of street lighting has reinforced doubts on the global applicability of the traditional 30% reduction figure.

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