A Government Accountability Office (GAO) study of five foreign ATC service providers contends that since “commercialization,” they have maintained safety, controlled costs and improved efficiency. The National Air Traffic Controllers Association emphasized that controllers in Cleveland alone handle more operations annually than all of Canada’s controllers handle. It is difficult to compare the U.S. National Airspace System with foreign systems, Rep. John Mica (R-Fla.) conceded. “The U.S. operates the largest and safest ATC system in the world and the U.S. has about 60 percent of the world’s air traffic activity.”