This report evaluates the quantity, quality, and availability of traffic accident and other safety-related data and their effects on the ability of Federal, State, and local governments to successfully perform highway safety missions. Practices in the collection, processing, and use of accident, traffic, and roadway inventory data in a sample of States and local jurisdictions are reviewed in terms of their impact on highway safety planning, implementation, and evaluation. The study notes the increasing use of microcomputers, the increased amount and quality of traffic volume and roadway inventory data, and the integration of traffic, roadway, and accident databases. Other findings include reduced reporting of property-damage-only accidents, increased numbers of tort liability claims, insufficient local data in State files, level of police training and interagency coordination, deficient local traffic and roadway inventories, and errors in the use of highway location reference systems. The study contains recommendations for accommodating and/or reversing some of these practices.