Forty-nine states now mandate seat belt use and motor vehicle fatalities have decreased. But there is more to the story. As more drivers used seat belts, fatalities for pedestrians and cyclists increased. Why? As seat belt use rose, driving became safer. As driving became safer, the cost to drivers of being inattentive fell. And as the cost of being inattentive fell, drivers could afford to exercise less care. So as safety regulations make drivers safer, pedestrians and cyclists face greater risk. —Antony Davies, James R. Harrigan