The National Transportation Safety Board relies on many external databases when performing accident investigations, safety studies, and special investigations. Most of these databases are sponsored and operated by the modal administrations of the U.S. Department of Transportation (DOT). The Board's ability to study important safety issues is often affected by poor data quality. The Board studied transportation safety databases to evaluate data quality issues and to encourage improvements in this area. The effort had four specific objectives: (a) highlight the value and potential uses of transportation safety data; (b) describe some accident and incident databases commonly used by the Board; (c) summarize past Board recommendations involving transportation data; and (d) evaluate Bureau of Transportation Statistics (BTS) efforts to establish data quality standards, identify information gaps, and ensure compatibility among the safety data systems maintained by the DOT.