In a recent Usenet exchange, a poster informed me that "The studies show that if you hit a pedestrian at 20mph there is a 95% survival rate, at 30mph it is 80%, at 40mph it is 10% (or 20% for a small child)." I found the size of the effect implausibly large, asked for a source, and was told that it was "A paper by Ashton and Mackay."