Casualty crash reductions from reducing various levels of speeding are estimated by applying the relative risk of involvement in a casualty crash to the proportion of vehicles travelling at a given speed. The greatest overall effect on casualty crashes involving vehicles travelling at speeds from 1 to 20 km/h above the speed limit will come from reducing speeds just above that limit in almost all cases. Analysis of where injury and fatal crashes occur indicates that while speed reductions of any type would be expected to reduce injuries and fatalities, the greatest potential gains for reducing injuries appear to be in targeting low level speeding on Adelaide low speed roads. For fatalities this would be extended to include low level speeding on high speed rural roads.