Updated

The new passenger screening program intended to speed up check-in times at airports has been expanded to 28 more major U.S. airports as the pilot continues to gain momentum and spread across the nation.

The U.S. Transportation Security Administration’s Pre-Check program has also added U.S. Airways (NYSE:LCC), United Airlines (NYSE:UAL) and Alaska Airlines (NYSE:ALK) to a short list of participating carriers that includes American Airlines and Delta (NYSE:DAL).

More than 336,000 passengers have already been screened through TSA Pre-Check, which enables passengers to undergo screening free of charge before they fly. After being identified as low risk, fliers acquire special passes that allow them to speedily pass through security without removing shoes or belts.

The initiative is intended to quicken check-in at airports while enhancing security by conducting a thorough screening on passengers that volunteer personal information, similar to a background check.

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TSA Administrator John Pistole said the expansion moves the U.S. farther away from the “one-size-fits-all approach to a more intelligence-driven, risk-based” system by recognizing that “most passengers do not pose a threat to security.”

The program, which has so far run through airports in Dallas, Miami, Las Vegas, Minneapolis, Los Angeles, Atlanta and Detroit, will expand into the new airports throughout 2012.

The three airports used to hijack planes during the Sept. 11 terrorist attacks - Boston Logan International Airport, Washington Dulles International and Newark International – are among the 28 to join.

Pistole said the data-driven program and all of TSA’s security initiatives are intended to “prevent terrorist attacks and reduce the vulnerability of the nation’s transportation system to terrorism.”

Since the TSA cracked down on security after 2001, it has confiscated some 50 million prohibited items such as tweezers and scissors. This year alone, it prevented more than 1,200 guns from being brought onto passenger aircraft.

Some other big-name airports include LaGuardia Airport and John F. Kennedy International Airport, both in New York, O’Hare International in Chicago, Philadelphia International, Ronald Reagan Washington National Airport and Lambert-St. Louis International Airport in Missouri.

The TSA, which calls itself a “U.S. government counterterrorism agency,” says it plans to continue expanding the program to additional airlines and airports once it deems them as operationally ready.

Not everyone is eligible to participate. Most are selected frequent flyers from participating airlines as well as members of Customers and Border Protection’s Trust Traveler programs, such as Global Entry and Nexus, who are U.S. citizens.

If an eligible person passes the TSA Pre-Check vetting process, information is embedded in the barcode of their boarding pass. From there, the passenger heads into the Pre-Check lane, where they undergo expedited screening, sometimes allowing fliers to keep their shoes, jackets and belts on, their laptops in their bag and toiletries in their carry-on.

The TSA says it is also testing other screening initiatives, such as a method to provide positive ID verification for airline pilots and the use of expanded behavior detection techniques.

Influential industry group The Global Business Travel Association applauded the TSA expansion and said it’s something members have been hoping for since the pilot was announced last summer.

"As an association, faster, more efficient and smarter travel processes that ensure the traveling public's safety are our top priority and essential for business travelers,” GBTA chief operating officer Mike McCormick said in a statement.

Other airlines expected to host the program by the end of the year include:

Baltimore/Washington International Thurgood Marshall Airport, Charlotte Douglas International, Northern Kentucky International, Denver International, Lauderdale-Hollywood International, Honolulu International, Indianapolis International, Louis Armstrong New Orleans International, Luis Muñoz Marín International, Orlando International, Phoenix Sky Harbor International, Pittsburgh International, Portland International, Salt Lake City International, San Francisco International, Seattle-Tacoma International, Tampa International, Ted Stevens Anchorage International and George Bush Intercontinental Airport.