The strongest relationship found was that for average road surface luminance: in the range 0.5-2.0 candelas/m2, it is estimated that an increase of 1 cd/m2 is associated with a 35 percent lower accident ratio. Other measures of luminance and illuminance were also found to be related to accident ratio, but not as clearly as was average road luminance, which is therefore the preffered explanatory variable. Analysis of pedestrian and non-pedestrian accidents separately did not reveal a relationship between the former and lighting quality. In contrast, non pedestrian accidents showed similar relationships to those for all accidents, with the addition of a possible relationship with overall uniformity of luminance