flights into and out of dca cannot be longer than . this rule is used to limit the number of aircraft over washington. it causes most of the air traffic to be sent to the washington dulles international airport which is larger and further from the city. there are some exceptions to this rule. in 2010, the airport served about 18.1 million passengers. reagan national is a focus city for american airlines. they are the airport's largest carrier. the american airlines shuttle has air shuttle service to laguardia airport in new york city and logan international airport in boston, massachusetts. delta air lines' delta shuttle also has air shuttle service to laguardia. these shuttle flights leave reagan international about once an hour. an exception to this rule permits 20 long-haul flights a day. most are from the west coast: non-stops from seattle, los angeles, san francisco, and portland oregon. however, san juan puerto rico is also part of this group. these exemptions were created in 2003 and 2012.