What You Need to Know About Those Long TSA Security Lines

— -- A recent apology from the Transportation Security Administration may fall on deaf ears this summer as airline passengers face growing security lines -- and frustration -- at airports.

TSA Administrator Peter Neffenger apologized to air travelers on Tuesday for the hours-long lines in Chicago responsible for leaving hundreds of passengers stranded at the city's airports overnight.

What happened? What can air travelers expect this summer? What is being done to shorten the lines and get passengers on their flights on time? ABC News breaks it down.

TSA: 'I Don't Know What That Was'

On Tuesday, Neffenger apologized for the extensive delays at Chicago's two major airports: O'Hare and Midway.

According to ABC-owned station WLS, about 450 American Airlines passengers scheduled to fly out of O’Hare International Airport Sunday night didn’t make it to the gate in time for their flights. Some said they waited two to three hours to get through the security checkpoints.

“We had a significant challenge in Chicago yesterday. I don’t know what that was. We’re fixing that,” Administrator Neffenger said during an event in in Houston. “I do apologize to the people who found themselves stranded in Chicago yesterday.”

He added: "We’ve got a team out there right now trying to figure out what the root cause of that were. We are not seeing that kind of problem throughout the system."

The hashtag #IHateTheWait is gaining traction on social media, but public security officials are unwilling to sacrifice safety for convenience.

“We want to keep passengers moving, but we want to keep passengers safe,” said Homeland Security Secretary Jeh Johnson. “That is our primary obligation.”

Airline Spokesperson: 'We Are Concerned About What the Summer May Bring'

Airlines for America, an airline industry trade organization, announced this morning that the June 1 to Aug. 31 travel period could see a record number of people taking to the skies, and thus passing through TSA security this summer.

Nearly 10 million more passengers are expected to fly in scheduled service on U.S. airlines during this time frame -- a fact unlikely to give comfort to flyers faced with long lines at the airport.

An American Airlines spokesperson told ABC News, “We are concerned about what the summer may bring.”

As air travel peaks during the summer, flights are very often full, making it difficult to reschedule those who might miss flights due to the waits.

Airlines Pitching In

Airlines for America says it's stepped up to the plate to ease wait times -- by allowing frequent flier miles to be used for TSA PreCheck and deploying employees to help with non-security functions (like moving bins, divestiture) at checkpoints -- but passengers are still facing “excessive” wait times.

American Airlines has dedicated $21 million toward providing such contract staff; $4 million more than the normal annual amount, according to an internal letter obtained by ABC News.

Two U.S. senators have asked airlines to stop charging bag fees during the summer. Sen. Blumenthal, D-Conn., and Sen. Markey, D-Mass., claim that the TSA has informed them that checkpoints serving airlines with bag fees see 27 percent more roller bags than those without the fees.

The TSA declined to confirm that statistic to ABC News.

The agency is urging the flying public to enroll in TSA’s PreCheck program, and it sounds like the public is listening.

More than 7,000 people signed up for the expedited security screening program this March -- almost 4,000 more than in March 2015. In fact, last week 10,000 people signed up on a single day, according to the TSA.

Airlines say they are asking the TSA to make more PreCheck appointments available and possibly even wave or reduce PreCheck fees.

Sharon Pinkerton, Airlines for America senior vice president of legislative and regulatory affairs, said, “It has been a challenging spring with fliers waiting in lines that take more than 60 to 90 minutes to get through security.”

One thing is for sure: Summer is coming.