More than 40,000 people die each year in motor vehicle crashes in the United States, and many more are seriously injured. Reducing this toll is a major goal of governments at all levels. Since the 1960s, the number of fatalities per mile driven has fallen by 75 percent owing to a combination of public and private actions to improve driver performance, motor vehicles, the highway environment, and postcrash emergency response and medical care. As a result, thousands of deaths and millions of injuries have been prevented. Nevertheless, the consequences of motor vehicle crashes continue to be a major public health problem and the leading cause of death among children and young adults. Continued growth in motor vehicle travel means that larger and larger improvements in crash rates are needed to produce any reduction in the total number of people killed and injured in crashes each year. Yet improvements in crash rates in the United States have been lagging behind those of many other developed countries.