Erin Sharp arrived at Baltimore-Washington International Thurgood Marshall Airport a little less than two hours before her 9:40 a.m. flight to San Diego on Sunday, timed so that her 11-month-old son would zonk out on the plane and they would arrive home with the afternoon to spare.

Instead, Sharp wouldn't leave the Anne Arundel County airport for another nine hours, she said, after an enormous ticketing line for Southwest Airlines caused her and other passengers to miss their flights and the airline couldn't immediately get her onto another.

"Southwest has this reputation for being the best and the fastest and the quickest," said Sharp, 34, who had been visiting her parents in Woodstock. "Instead, it was like paralysis."

In recent weeks, the airline — the largest at Baltimore's "easy come, easy go"-branded airport — has run into major peak-hour problems, with summer vacationers tripping over business travelers in ticketing and security lines that at times have intermingled, creating confusion, airline and airport officials said. The congestion's been compounded by Transportation Security Administration staffing declines and a decision to close one of the airport's security checkpoints to minimize the mixing with long check-in lines.

"The issue is the volume of people that we're seeing," said Paul Wiedefeld, the airport's executive director. "It's a symptom of a very strong business, a very strong summer."

Thais Conway, a Southwest spokeswoman, said the airline is experiencing a "typical seasonal increase in traffic during the peak travel periods" but is working with the airport and the TSA to find solutions.

The TSA, meanwhile, is dealing with its own challenges, including budgetary restraints that have translated recently into a decline in the agency's national workforce, through attrition, of between 6 percent and 7 percent, said TSA spokeswoman Lisa Farbstein.

While BWI's TSA staff likely shrank similarly, Farbstein said that's not the reason for the airport's long summer lines. But the agency, she said, is working with Southwest and BWI to find a solution.

Recently, Southwest ticketing lines got so long they began encroaching on the nearby security checkpoint for Concourse B, raising security concerns from the TSA.

"People who thought they were getting in the line to go through the [security] checkpoint found they were in the line to go check in [with the airline], although they didn't need to because they already had their boarding pass," Farbstein said.

Officials responded by closing that checkpoint during morning rushes and moving the TSA agents assigned to it to the next checkpoint down, for Concourse C

The checkpoint for Concourse C is new and wide, with extra, unused lanes the agents could slide into. It is connected to Concourses A and B behind security, though airport officials said many fliers may not know that, in part because it is out of sight of the Southwest ticketing counters.

Both Concourse A and Concourse B are dedicated to Dallas-based Southwest, which along with subsidiary AirTran is responsible for more than 70 percent of traffic at BWI. Conway said the airline's integration of AirTran flights at BWI, including some to international destinations, has not contributed to the longer lines.

Both airport and airline officials said even with the Concourse B checkpoint closure, the number of security lanes has remained the same and average wait times have remained about 20 minutes. They said spreading Southwest crowds across more of the terminal has helped alleviate crowding.

But some passengers see the unannounced closure more as a driver of congestion than a solution to it.

"I plan on having all three checkpoints open. It helps disperse the load of travelers," said Zack Wolfe, 30, an insurance investor who lives in Owings Mills and flies to upstate New York for business every Monday morning. "You run such a fine line at the airport these days trying to make planes and get through security. … When you show up not knowing when one of [the] checkpoints is going to be closed, that makes a big difference."

Wolfe said more transparency on the part of the airport and Southwest would be appreciated, both about the morning checkpoint closures, which officials say are temporary, and about any permanent solutions being considered.

"It's not like I can take my business elsewhere," he said. "BWI is the airport in the area that makes the most sense."

Officials with BWI, Southwest and the TSA said they are working on it.

Wiedefeld and Conway said they are collaborating to direct more existing Southwest passengers to the Concourse C checkpoint, which Conway said will "help the flow of traffic" around Southwest's ticket counters and improve wait times.