More people ride L.A. Metro's rail lines on any given weekday — nearly 360,000, on average — than fly through Los Angeles International Airport on a busy day. Yet rail commuters go through virtually none of the body scanners or metal detectors that are common at LAX.
Officials with both L.A.'s transit agency and the federal Transportation Security Administration are now testing technology with the potential to change that — without forcing transit riders to wait at airport-style security checkpoints.
Since September 2017, officials with the transit agency have been testing "passive" body scanners: heat-sensitive screening technology that allows a law enforcement officer to scan passers-by for weapons or explosives before they ever go through a turnstile or board a train.
With TSA officials on-hand, Metro officials conducted their latest test of a passive body scanner on Tuesday, aiming two of the devices at morning rush commuters on an escalator and staircase leading into the bustling Seventh Street-Metro Center station.
Most of the commuters who entered the scanner's field of vision appeared as green, amorphous blobs on the screen of a laptop — the scanner is calibrated to display the natural heat waves emitted by the human body without revealing too many intimate anatomical details.
But several officials tested the system Tuesday morning by wearing objects under their shirts emulating an explosive device. When they entered the device's field of vision, the hidden objects showed on the scanner's screen as black masses in the center of their green-colored bodies.
The idea, officials say, is that law enforcement officers can use these test results to identify someone who might be carrying something dangerous and then pull that person aside for further screening, said TSA spokeswoman Lorie Dankers.
"You can use all of those layers of security to keep the entire system safe and secure, and this is one of those layers," Dankers said.
Metro spokesman Dave Sotero said this is the third test the transit agency has conducted of passive scanners since September 2017 — all part of an effort to find technology that will be most effective in "helping us to reduce our vulnerability to terrorism."
TSA has partnered with transit agencies all over the country to test these scanners — among them: Amtrak, San Francisco's BART, New Jersey Transit, and the Washington, D.C., Metro. TSA has also deployed these scanners at several high-profile events, from political conventions and the presidential inauguration to Pope Francis' visit and the 2014 Super Bowl.
The use of this passive scanning technology raises several tricky legal questions, says Eric Miller, a professor at L.A.'s Loyola Law School who specializes in policing issues.
Miller pointed to the pending Carpenter v. U.S. case as evidence that the Supreme Court is worried about "big data transforming our notions of privacy" and about "mass collection of data using passive monitoring systems." While Carpenter deals with cell phone data collection, Miller said there's an argument that passive security screening in transit terminals isn't that much different.
Miller credits the transit agency for exploring technology that could minimize the possibility for racial profiling — even though the technology doesn't eliminate that possibility altogether.
Still, on a more basic level, "think about what they’re doing," Miller said. "They're deploying a device that shows a mass on an individual’s body and backpack" — and, he argued, evidence of a mass on someone's body is not on its own enough to give a police officer probable cause to conduct a search.
"That strikes me as an incredibly crude way of trying to work out whether people are carrying dangerous devices," he continued. "It only benefits us if there’s a lot of other evidence that would suggest that a particular station is currently vulnerable or not. Otherwise they’re just doing mass data collection of individuals."
Officials with the transit agency are still only testing the technology and have not yet made a decision on whether to bring the passive body scanners into broader use — a decision that would come with its own logistical challenges.
"What happens when something gets picked up?" noted Susan Walker, Metro's director of physical security. "If we only do half the job by setting the machines out, we're not following through with what we need to do."
That follow-through is "very manpower intensive," Walker said.
In order to perform that follow-through well, she said Metro really needs LAPD officers on-hand while it conducts passive screening — LAPD officers after all, have bomb-sniffing dogs and broader enforcement authority. Metro employs transit security officers, not sworn police.
While overall crime on L.A.'s transit system has declined recently, Metro has received more reports of serious or violent crimes in the last six months, according to a KPCC analysis. Metro officials attribute the increase to a stepped-up law enforcement presence on buses and trains during that period.