Transportation Security Administration officials have tested the portable screening technology to detect explosives and other weapons for years, including at Union Station in Washington on May 9. (Transportation Security Administration)

A portable version of those airport body scanners that travelers loathe might soon be used to screen commuters at subway and bus stations across the country.

The Los Angeles County Metropolitan Transportation Authority announced in August it will become the first to deploy the technology this fall, adding an extra layer of security to the country’s third-largest transit system. Amtrak and New Jersey Transit are considering it, officials said. The system has been tested at Washington’s Union Station.

Los Angeles International Airport is exploring its use in pre-security checkpoints. And more major transportation agencies may incorporate similar technology as they harden their properties against threats, experts say.

Safety and security experts say the “stand off explosive detection technology” is a significant breakthrough in the era of rising threats against public transportation. The high-tech devices cannot only detect weapons to stop attacks and potentially save lives, they say, but also serve as a deterrent. Officials say, for example, the technology might have prevented a pipe-bomb detonation that injured five people at the Port Authority Bus Terminal in the heart of New York in December.

“An added layer of protection like this makes terrorists think twice about strapping a bomb to themselves,” Denver-based security consultant Autumn Harris said.

“We want to continue to make it harder for those who seek to do harm to our customers, employees, equipment and facilities,” Amtrak spokeswoman Kimberly Woods said.

But the devices also have raised concerns among some civil liberties and privacy advocates who fear the technology might be misused and question whether screening everyday commuters in the name of security goes too far.

The American Civil Liberties Union this week filed a public records request demanding more information about the body scanners, which the group says raise “serious constitutional questions.”

The technology

The Thruvision suicide-vest-detection technology reveals a suspicious object on a man during a TSA demonstration in New York’s Penn Station in February. (Richard Drew/AP)

During a recent chaotic morning rush hour at Washington’s Union Station, officers from Amtrak and the Transportation Security Administration sat behind a set of computer screens while the body scanners — one on a tripod and the other in a rolling case — monitored passersby in the city’s busiest rail station.

As commuters walked past, the devices scanned their bodies, detecting any anomalies. The scans can capture images as far as 40 feet away, officials said. The technology is designed, for example, to detect suicide vests or other strapped-to-the-body explosives.

“They will trigger an alarm on a laptop screen if someone is wearing an improvised explosive device as that person walks by the unit. It can detect both metallic and nonmetallic threats by identifying items that block the naturally occurring emissions emitted by a person’s body,” TSA spokeswoman Lisa Farbstein said. “No radiation of any kind is emitted, and no anatomical details of a person are shown on the laptop screen.”

Alex Wiggins, chief security and law enforcement officer for the Los Angeles Metro, said the agency is not intending to screen down to the level of cellphones and other metal objects carried by passengers.

“We are very specific about what we are looking for,” Wiggins said. “We are looking to screen for weapons that have the potential to create mass casualties. Explosives, suicide vests, assault weapons, things of that nature.”

A Los Angeles sheriff's department deputy and his K-9 and LAPD officers stand next to the Thruvision detection technology that reveals suspicious objects on people at Union Station in downtown Los Angeles in August. (Richard Vogel/AP)

Unlike the stationary body scanners used by TSA agents at airport checkpoints, these devices are mobile.

The government has been working on the technology for more than a decade, dating back to the 2004 Madrid train bombings that left nearly 200 dead. The TSA tested it at New York’s Penn Station and Washington’s Union Station before clearing it for agencies to purchase. The TSA has used the portable devices to secure large-scale events, such as the Super Bowl and the pope’s visit in 2015.

Other transit systems are interested in the technology but say the cost is prohibitive. The device costs about $100,000. While that might not sound like much in a multimillion- or billion-dollar budget, many of these agencies are already struggling to cover basic operating and capital needs for their aging systems.

San Francisco transit officials said they have not even considered the technology because they lack the personnel who would be needed to run the system. The Washington Metropolitan Area Transit Authority has not tested it and is not considering it, an agency spokesman said. But the agency’s board chairman said he’d be interested if money wasn’t an issue. The city’s subway, with 91 stations and 117 miles of track, is the second-busiest in the country.

“Price is an issue with the Washington Metro because we are strapped for cash,” Metro board chairman Jack Evans said. “It would be nice if the federal government would pay for it. They certainly do it in airports, and there are a lot more airports than there are transit systems.”

The TSA is not purchasing the technology to give to agencies, Farbstein said. It is only facilitating the opportunity for them to test it.

But funding for such programs is scarce. Agencies are competing for federal transit security grant money that has been dwindling in recent years, said Polly Hanson, director of security, risk and emergency management at the American Public Transportation Association (APTA).

Federal transit security funds went from roughly $253 million in fiscal year 2010, to $88 million this fiscal year, according to APTA.

In December, Sen. Charles E. Schumer (D-N.Y.) urged the TSA to speed up the testing of the devices to make them accessible to law enforcement and transit agencies, saying they belong in rail systems such as the New York subway.

“We not only want these devices in America’s busiest cities, like New York, but we need them here,” Schumer said.

“If they work as well as touted, pursue an expedited seal of approval that gives all of us another layer of security to fend off would-be lone-wolf terrorists,” he said. “As the threats we face evolve, our preparedness and response must evolve as well to remain a step ahead of evildoers.”

While the devices have been tested in New York’s Penn Station, transit officials declined to comment on system security plans.

Safety vs. security

The 2004 Madrid train bombings and the attacks in London’s Underground a year later heightened the need for bomb detection measures and electronic surveillance. The portable body scanners are the latest addition to security protocols already in place, such as random bag checks, field officers and dogs that can detect explosives.

“We know that we cannot attempt to impose an airport model of security on the public surface transportation systems,” said Brian Jenkins, director of security research at the Mineta Transportation Institute. “The volumes of passengers on surface transportation are far greater than the numbers at airports. It would require a force of hundreds of thousands of screeners if we attempt to do this in the United States.

“It would cause unacceptable delays. People may be okay with waiting at airports to board long flights, but they are not going to be willing to put up with lengthy delays two times a day during their commute, and the cost would be prohibitive.”

There’s also the question of how to handle a threat, once found. And there are privacy concerns. How much freedom are Americans willing to give up in the name of safety and security?

“Someone is not going to shout out, ‘Hey, you, with a bomb, can you step aside please?’ ” Jenkins said. “So how do you handle that in a way that does not imperil the safety of others and in a way that (respects) the liberties of individuals.”

Jay Stanley, a senior policy analyst at the ACLU, said there are a number of questions about widespread use of the technology, from whether people will be allowed to opt out of screening to the technology’s ability to differentiate between a weapon and items like money belts and personal medical devices such as colostomy bags.

“To what extent are we going to turn ourselves into a garrison state and embrace the airportization of the American life?” Stanley said. “We shouldn’t let these security bureaucracies march forward without having an open forum of discussion of this technology and what it can and cannot do.”

While body scanners are used in airports because of an “administrative exception” to the Fourth Amendment that the courts have found is reasonable because of the unique security vulnerabilities of aircraft, he said it is far from clear that the courts will permit this exception to expand to cover crowded public places such as transit stations.

“If I have a medical appliance under my body, do I have to worry every time I am in public transit that I am going to get hassled by security people because I am an anomaly to them?” Stanley said. “If I feel like I can’t put a money belt on or carry some valuables in my bra without feeling like somebody is going to jump all over me for that, then I have become less free.”

Experts say agencies and the public might have to do a ­cost-benefit analysis.

“There is no allusion that we can stop every single terrorist attack in the country or that we can protect every single target,” Jenkins said. “Terrorists can always have the advantage. . . . But what we can try to do is to mitigate that risk both through deterrent and by increasing our chances of detection.”