• This doesn’t really apply because harm to a pedestrian during an impact isn’t a linear scale.

      There are sharp decreases in fatalities and permanent injuries, particularly to children who are often the ones hit in neighbourhood streets, below about 30 km/h so there’s a strong incentive to have drivers travelling at speeds no higher than that to avoid child murder and maiming due to inattention.

      Below those speeds, and given that people do often belatedly apply the brakes when they’re driving recklessly there is a much weaker case for further reduction in speed limits. At least until car geometry changes again to make them even deadlier /shrug shrug