NEW YORK ( TheStreet) -- Washington's two airports seem headed in different directions.
Traffic at Reagan National Airport has been flat but now is growing in the wake of the 2013 merger of American (AAL) and hub carrier US Airways.
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Meanwhile, traffic at Dulles International Airport has been declining for the last four years, a trend that seems likely to continue as hub carrier United (UAL) downsizes and the per-flight cost of operating at the airport climbs.
"The National passenger volume was dropping because AA/US took out flights faster than the slot buyers put them in, but that's changing now," said aviation consultant Sandy Rederer, who has studied the Washington area airports.
At National, seats per flight will have increased to 99 in January 2015 from 92 in January 2014, according to statistics compiled for TheStreet by Ron McNeil of Mead & Hunt.
In November, the Justice Department required American and US Airways to divest 52 slot pairs at National. Low-fare carriers JetBlue (JBLU) , Southwest (LUV) and Virgin America all won the right to purchase slots, which enable flights at specified times at the congested airport. The carriers are flying mainline jets, in many cases replacing regional jets flown by US Airways.
"National slots were underutilized by US Airways with way more than 100 daily departures on 50-seat and smaller aircraft," Rederer said. "That's changing, though I'm surprised by how slowly the transition has progressed.
"The January 2015 schedule shows 273 more departures than in Jan 2014," possibly a reflection that the slot buyers offer more weekend flights than American and US Airways did, he said.
One theory has it that by enabling low-fare carriers to operate at National, the Justice Department discouraged them from operating at Dulles and contributed to declining traffic there.
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