By Alison Hill
20 mph saves lives. The likelihood of severe or fatal injury to a pedestrian struck by a driver is 17% at 20 mph, 30% at 25 mph and 47% at 30 mph. There are 7–10 times fewer fatalities if a collision occurs at 20 mph compared to 30 mph. Inevitably, people make errors of judgement on roads, but those errors are less serious at slower speeds.