Southwest Airlines will more than double its presence at Ronald Reagan Washington National Airport by the end of the year, the Dallas-based carrier announced last week.

The airline plans to add 27 daily flights to its current line-up of 17 daily flights in the latest round of changes, a byproduct of the merger of American Airlines and U.S. Airways.

“Reagan has long been a convenient but high-fare airport,” Gary Kelly, chairman, president and chief executive of Southwest, said in a statement. “Southwest plans to change that.”

Southwest said the airline’s new destinations and schedules will be announced by the end of this quarter. The flights are expected to be up and running by the fall.

The Justice Department ruled in November that American Airlines had to give up at least 104 slots — enough for 52 round-trip flights — at Reagan National. The idea, officials said, was to give low-cost carriers a chance to compete in major markets and drive down prices for consumers.

“The department’s ultimate goal has remained steadfast throughout this process — to ensure vigorous competition in airline travel,” Attorney General Eric Holder said at the time.

JetBlue Airways said it has received rights for an additional 12 round-trip flights per day at Reagan National, bringing its total to 30 daily flights by the end of this year.

The changes still await approval by the Justice Department. A handful of round-trip slots remain up for grabs.

The musical chairs at Reagan National could bring up to 2 million additional passengers to the airport every year, according to the Metropolitan Washington Airports Authority.

More than 20 million passengers flew through Reagan National last year, up roughly 30 percent from previous years, according to MWAA.

“The increase in passengers at Reagan National is being driven largely by regulatory decisions that have prompted some airlines to switch flights from Dulles [International Airport] to Reagan,” said Jack Potter, president and chief executive of MWAA, which oversees both airports.

A number of changes unrelated to the American Airlines merger have also taken place in recent weeks. Frontier Airlines announced it will stop offering flights from Reagan National to Kansas City; Madison, Wis; and Omaha, Neb., as a result of its split from Republic Airlines, which owns those slots.

Southwest, meanwhile, on Saturday began offering a temporary daily flight between Reagan and Kansas City. (The Transportation Department is in the process of finding a permanent operator for the route.)

American Airlines, which still operates more than half of the flights out of Reagan Airport, no longer offers daily service from Reagan National to a dozen U.S. cities, including Detroit, Omaha and San Diego. It did, however, add a second daily flight from Washington to Los Angeles.

Southwest’s growth at Reagan comes at a time when it is already the dominant airline at Baltimore-Washington International Marshall Airport. Southwest is in the process of digesting its own merger after it acquired AirTran Airways. As a result, Southwest recently announced plans to take over some AirTran international routes on July 1, offering flights between Baltimore and Aruba, the Bahamas and Jamaica.

The Southwest and AirTran account for more than two-thirds of BWI passengers.