National Transportation Safety Board is a United States federal agency that investigates transportation accidents and issues safety recommendations. The agency, sometimes called the NTSB, maintains a database on all accidents involving civil aviation (the operation of nonmilitary aircraft) in the United States. It also investigates significant highway, marine, pipeline, and railroad accidents that occur in the nation. The NTSB aims to restore the safety of transportation systems following accidents and to prevent future accidents. The agency also conducts independent studies and monitors organizations, procedures, and programs that affect transportation in the United States.