Air traffic demand is increasing, but capacity is constrained by an antiquated air traffic control (ATC) infrastructure. The number of air traffic passengers in the U.S. is expected to grow from 738 million in 2005 to 1 billion in 2015. The number of commercial airline flights is expected to grow from 13 million in 2005 to 15 million in 2015. [22] Figure 1-1 shows the growth in air traffic demand in the United States in recent years.This research was funded by the Federal Aviation Administration's Surveillance and Broadcast Services program under contract DTFA01-C-00030