With a program that started Tuesday, some frequent fliers can keep on their shoes, belts and jackets when going through airport security in Atlanta.

The Transportation Security Administration launched a pilot program called "TSA PreCheck" for expedited security screening in Atlanta, Detroit, Dallas/Fort Worth and Miami.

In Atlanta, the "trusted traveler" type program is for Delta frequent fliers who travel often, are U.S. citizens, are deemed eligible for the program and who opt in. When they are flying domestically, they are directed to the South security checkpoint at Hartsfield-Jackson International Airport, where they might be instructed to go through the single lane designated for expedited screening. A traveler won't know for sure until that point.

The lane has a metal detector rather than a full-body imaging machine.

In that lane, a sign tells travelers that there's no need to remove shoes, belts, light outerwear, and bags of liquids that are compliant with TSA restrictions.

"We know it's significantly faster," said TSA assistant administrator Christopher McLaughlin. Still, "Nothing will ever guarantee that a traveler will receive expedited screening."

The agency said it will continue to use random and unpredictable security measures throughout the airport and multiple layers of security.

Some members of other trusted traveler programs through U.S. Customs and Border Protection, including Global Entry, SENTRI and NEXUS, are also eligible to participate if they are U.S. citizens and flying on Delta or American.

The TSA expects as many as 2,000 people will participate in Atlanta daily, and a total of 5,000 to 8,000 nationally, as the pilot program in partnership with Delta and American develops. The agency screens about 55,000 passengers in Atlanta daily and about 1.7 million passengers nationally.

The expedited screening is part of a broader move by TSA "away from a one-size-fits-all approach," along with special procedures for airline crew members and children. The idea is to focus efforts on passengers the TSA knows the least about and those on terrorist watch lists.

The agency will study the efficiency and security effectiveness of the TSA PreCheck program for at least 60 days to determine whether to roll it out nationwide to more airlines, airports and travelers.