CHARLOTTE, N.C. -- The nation's long-inadequate aviation infrastructure will get a major upgrade next month, when new runways open at three key airports, including Chicago's O'Hare International. O'Hare, a hub for both AMR's ( AMR) American Airlines and UAL's ( UAUA) United, is one of the system's key chokepoints, and the third-worst airport for delays in the U.S. during the first eight months of the year. Only 64% of flights arrived on time. The new runway means O'Hare will have three sets of parallel runways, enabling it to offer three simultaneous departures, even in bad weather. New runways will also open at Washington's Dulles International, another United hub, and at Seattle-Tacoma International, a growing international gateway and a hub for Alaska Air ( ALK). Operations at both of those airports will benefit, but neither needs the sort of help in relieving congestion that O'Hare requires. The last time O'Hare opened a new runway was 1971, when U.S. airlines carried about 174 million passengers, or roughly 23% of the total in 2007. The hub system then was in its infancy, marginally in use by Delta ( DAL) in Atlanta, and the associated operational peaks and valleys were relatively rare. After a new runway opened in Atlanta in 2006, Delta boosted its hourly departures and arrivals by 25% to 35% and saw its on-time performance improve. In 2004, the Federal Aviation Administration imposed caps that limited O'Hare to 88 departures an hour at peak travel times. Those caps expire Friday night. Because flight caps are being lifted in Chicago, American and United disagree on just how much of a benefit the new runway at O'Hare will provide. This month, United operated about 600 daily O'Hare departures, while American had about 420.