The American Association of State Highway and Transportation Officials (AASHTO) has adopted a national highway safety goal of halving fatalities over the next 2 decades; or reducing fatalities by 1000 per year. This goal can be achieved through the widespread application of low-cost, proven countermeasures that reduce the number of crashes on the nation's highways. This twenty-first volume of NCHRP Report 500, "Guidance for Implementation of the AASHTO Strategic Highway Safety Plan," provides guidance on data sources and analysis techniques that can be employed to assist agencies in allocating safety funds. The report will be of particular interest to safety practitioners with responsibility for implementing programs to reduce injuries and fatalities on the highway system.