Hartsfield–Jackson Atlanta International Airport now the airport's second largest carrier. In May 2001 construction of an over fifth runway (10–28) began. It was completed at a cost of $1.28 billion and opened on May 27, 2006. It bridges Interstate 285 (the Perimeter) on the airport's south side, making Hartsfield–Jackson the nation's only civil airport to have a runway above an interstate (although Runway 17R/35L at Stapleton International Airport in Denver, Colorado crossed Interstate 70 until that airport closed in 1995). The massive project, which involved putting fill dirt eleven stories high in some places, destroyed some surrounding neighborhoods and dramatically changed the scenery of
Stapleton International Airport Western began flights to Calgary. The Boeing 747 was introduced to Stapleton on Continental's Los Angeles route in 1970. In the early 1970s, Frontier occupied Concourse A, United occupied most of Concourse B, and Western and Continental occupied most of Concourse C. United and TWA served both coasts nonstop during this era, while Continental and Western's nonstop flights only extended to the western half of the country. Concourse D was built in 1972. After deregulation, Denver's four major incumbent airlines developed hubs at Stapleton. United occupied Concourse B, Continental and Western occupied Concourse C and Frontier occupied Concourse D. Western