San Diego International Airport, also called Lindbergh Field, is an international airport 4.8 km northwest of downtown San Diego. In 2015, traffic at San Diego International went beyond 20 million travellers for the first time. It is the busiest single-runway airport in the US. It is likewise the second-busiest single-use runway worldwide after London's Gatwick Airport. San Diego is the biggest city in the United States that is not an airline hub or secondary hub; nevertheless, San Diego is a focus city for Southwest Airlines. The airport has domestic flights, and worldwide flights to Canada, the United Kingdom, Mexico, and Japan.