The National Transportation Safety Board (NTSB) is an independent U.S. government investigative agency responsible for civil transportation accident investigation. In this role, the NTSB investigates and reports on aviation accidents and incidents, certain types of highway crashes, ship and marine accidents, pipeline incidents, bridge failures, and railroad accidents. The NTSB is also in charge of investigating cases of hazardous materials releases that occur during transportation. The agency is based in Washington, D.C. It has four regional offices, located in Anchorage, Alaska; Denver, Colorado; Ashburn, Virginia; and Seattle, Washington. The agency also operates a national training center at its Ashburn facility.