By Keith Laing - 03/10/11 08:28 PM EST
Southwest Airlines carried the most domestic passengers in December, totaling 8.9 million. American Airlines led in international travel, carrying 1.7 million people overseas.
For the year, Delta Airlines led both domestic and international travel, with almost 11.1 billion domestic “enplaned passengers” — which includes trips with layovers (meaning they're counting each time a person boards a plane — and 20.9 million international enplanements.
Atlanta's Hartsfield-Jackson airport was the busiest airport in December, with 3.4 million passengers. It was followed by Dallas/Fort Worth, with 2.2 million travelers. For the year, Atlanta led with 42.5 billion, followed by Chicago's O'Hare International Airport, with 30 billion.