Dulles is more likely to draw from Washington west into Virginia, as far away as Charlottesville and Richmond, Jenkins said. There isn't another Southwest airport in Virginia for about 200 miles, in Norfolk.
Other carriers at Dulles will have some insulation against Southwest because they have customers entrenched in their frequent flier programs and offer amenities such as business and first-class cabins and in-flight entertainment. They also offer international service, and Southwest does not.
At BWI, Southwest controls about half the market with about 172 daily flights, many times the 12 planned at Dulles, and BWI officials say they still expect passengers to come from the Washington area. According to airport surveys, about half of its passengers drive from the Washington area.
BWI officials point out that the airport has continued to grow as Southwest has expanded in Philadelphia, even though about 15 percent of BWI passengers come from Pennsylvania.
In July, Southwest's monthly total exceeded 1 million passengers at BWI for the first time, up 6 percent from July 2005, said Jonathan Dean, a BWI spokesman. The airline again exceeded 1 million passengers in August, up 8 percent from August 2005.
In addition to the Washington area, Southwest saturates the Boston area with flights from Manchester, N.H., and Providence, R.I. That's also the case in the Los Angeles area, where Southwest flies from Los Angeles, Burbank, Ontario and Orange County. In the San Francisco area, it serves Oakland and San Jose. (The airline pulled out of San Francisco's airport in 2001 after 19 years, blaming flight delays.)
Southwest's Sweet said the airline has managed to add service at all of the other airports over time because its fares attract more people to travel - something the U.S. Department of Transportation dubbed the "Southwest effect." Also helping have been the record number of people flying and an Internet-fueled shift to low-cost carriers.
For their part, Dulles officials say the airport felt a void when Independence left. The number of domestic passengers at Dulles dropped to 1.02 million in July, from 1.54 million in July 2005.
"We knew from the beginning that Independence was not going to sustain the numbers," said Tara Hamilton, an airport spokeswoman. "They offered 600 flights, and that's highly unusual to introduce service with that many flights a day. What Independence did prove is that there is a tremendous market for low fares out of Dulles. And people and businesses continue to move in."
Southwest's success at Dulles - and BWI - will be up to passengers. They began booking Dulles flights online a few weeks ago and at the airport's recently overhauled ticket counter a few days ago. Some frequent fliers said price, convenience and perks would be factors driving their decisions.
William Beck, who lives about a half-hour from Dulles, said he can drive to BWI in about an hour to fly Southwest. That's something he did before Independence moved into Dulles and forced competitors to lower prices. It's something he expects to do again now that Independence is gone. He has a BWI flight scheduled in November.
"If [United Airlines) matches Southwest's prices, I will fly UA," he said. "If UA does not match, I will fly Southwest from Dulles. For destinations that require me to go to BWI, I will assess the trade-off of driving versus the cost savings I would receive from using Southwest as opposed to UA."
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