Bart Jansen

USA TODAY

WASHINGTON – Three years, more than 1,000 comments and multiple challenges by advocacy groups later, the Transportation Security Administration issued a rule Wednesday finalizing its policy for using full-body scanners at airports.

While TSA insists the machines are the best way to protect the nation's travelers from terror attacks, critics challenge the use of devices over privacy and health concerns. The legal battle went all the way to an appeals court, which said TSA could keep the machines if it took legal steps to justify their use.

In a 157-page report that summarizes arguments for and against the machines, and their hefty price tag — $2.1 billion from 2008 through 2017 — the agency said the devices provide “the most effective and least intrusive” way to search travelers for weapons hidden under their clothes.

And with that, the agency finalized its regulation governing the machines. The rule won't change anything for travelers. Even as the question wound its way through courts, TSA deployed the machines and now uses 793 full-body scanners at 157 airports.

Despite the administrative finality, critics say they will still fight to dismantle the machines. Marc Rotenberg, president of the Electronic Privacy Information Center, said Congress should hold hearings on the rule.

“The agency has simply ignored what the public said,” Rotenberg said. EPIC filed a lawsuit that led to the removal of X-ray devices, known as "backscatter" machines, that were used from 2008 to 2013.

In March 2013, the U.S. Court of Appeals for the D.C. Circuit ordered TSA to justify use of a different version of machines called "millimeter wave" scanners, with a formal rulemaking. Sifting through and responding to more than 1,000 comments from the public took years, TSA officials said.

Marc Scribner, a fellow at the Competitive Enterprise Institute, a non-profit group that advocates limited government, said all the pages and all the words fail to justify using equipment many travelers oppose. His group, which sued TSA for deploying the machines without a formal rule, is evaluating its next move.

“The TSA simply fails to understand the extent to which people dislike body scanners,” Scribner said. “The TSA raised more questions than answers. We’re not particularly satisfied.”

Travelers complained the machines are so off-putting that they would rather ride Amtrak than fly. Others claimed the scanners created tension between travelers and TSA officers. The agency said 1% of travelers have opted for pat-downs to avoid the machines.

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TSA says the scanners add another layer of security at checkpoints besides metal detectors, explosives-detection systems and bomb-sniffing dogs. For example, a ceramic knife might not trip a metal detector and might not have an explosive scent for a dog to detect.

The threats the machines could have detected include the shoe bomb Richard Reid attempted to detonate on an international flight to the U.S. in December 2001, Umar Farouk Abdulmutallab's underwear bomb on an international flight in December 2009 and two non-metallic explosives in Yemen printer cartridges in October 2010, the agency's ruling said.

The full-body scanners used in all airports since May 2013 are called "millimeter wave" machines, which bounce electromagnetic waves off the traveler to provide an animated image where a suspicious item might be located. The TSA no longer uses the backscatter scanners that produced near-naked images of travelers.

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If a suspicious item is detected, TSA officers pat down a traveler to see what it is.

“I consider it one of the most effective means of determining and detecting whether somebody is moving a non-metallic device through the system,” TSA Administrator Peter Neffenger told a Senate Appropriations subcommittee on Tuesday.

Besides detecting non-metallic weapons, the machines hasten screening because a traveler moves through faster than a pat-down. A traveler can usually request a pat-down to avoid a full-body scanner. TSA revised the estimated average time for a pat-down to 150 seconds from 80 seconds because of waiting for a same-sex officer to perform the search.