a retrospective study of accidents in the dark reported before and after installing new or improved street lighting at 43 sites on trunk roads has been carried out, with particular attention to the effects associated with different speed limits. changes in dark accidents for the trial lengths were compared to the number of accidents occurring in darkness on the remainder of the trunk and class 1 roads having the same speed limit and within the same police district. on this basis statistically significant changes in accidents in the dark have been established only on the group of 19 roads with a 70 mile/h speed limit, where the reduction in dark accidents was of the order of 50 per cent. the non-significant changes found on roads with other speed limits were about 15 percent reduction both on 30 mile/h roads (10 sites) and 40 mile/h roads (7 sites), and about 50 per cent increase on 50 mile/h roads (7 sites). for each speed limit group except 40 mile/h the change in fatal and serious accidents was greater than the change in all injury accidents. on the basis of costs obtaining at the time of the installation of lighting the saving in costs of accidents on the 70 mile/h roads was about three times the annual cost of the lighting. (a)

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