Critics compare BART’s new double-decker fare gates to a guillotine. Supporters call them a necessary innovation. Some riders simply recoil at the design: two gates stacked vertically with one at waist level and the other at the average adult’s shoulders.

Tamar Allen, the agency’s assistant general manager of operations, fiercely defended the model that engineers installed June 9 at Richmond Station.

So far, no one has been injured, said Allen, who is carefully keeping tabs on the experiment — she watches patrons enter the station from a video monitor at her office. But many are intimidated by the equipment, which represents BART’s latest effort to stave off fare cheats.

It’s far from perfect. Eight people sneaked through between 2:30 and 3:30 p.m. on Friday, some by “piggybacking” behind other riders; others by squirming between the upper and lower triangles of the closed gates. One person slipped through an emergency side gate, and another scaled a railing that maintenance crews had raised several feet, hoping to deter climbers.

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Yet if the new stacked barriers don’t entirely solve BART’s fare evasion problem, they seem to work as a scare tactic, similar to the ramped-up police patrols assigned to the downtown San Francisco stations during rush hour. As the agency grapples with an epidemic that siphons $25 million a year and begets other forms of lawlessness, such as petty theft and drug use, officials want to send a stern message to riders.

“We want people to realize that it’s not acceptable to cheat on fares,” said spokesman Jim Allison. “We’re trying to change the culture.”

As Allen and other officials stood watching on Friday, a woman pushing a stroller let out a high-pitched yelp when the gates cinched closed behind her. Some commuters scurried through, while others glanced anxiously over their shoulders as the wedges slammed shut.

“If you really want to get hit, and you work at it, then yes, you may get hit,” Allen said. “But you have to work at it.”

The new gates are connected by steel rods on both sides, so they move as a unit — when an upper wedge hits something, it stops the lower wedge as well, and vice versa. And they’re designed to strike the widest part of a person’s body, Allen said. So even if people stop in the middle of an entryway to intercept the rods, they’re unlikely to get hurt.

She demonstrated by standing inside a gate, allowing the panels to snap out and press into her sides. The top barrier sandwiched Allen’s upper body while the lower barrier pushed her wrists.

“And I can easily push them back,” Allen said, knocking the wedges back into the metal cabinets that form a passageway just wide enough for a barrel-chested rider, or a person carrying luggage.

Riders have mixed reactions. Some wheelchair users worry that the upper consoles will close on their heads or necks. Able-bodied commuters have similar gripes: Joe Martinez of Richmond complained loudly that a gate “damn near hit me on the shoulder” as he walked through. Systems maintenance superintendent Randy Radford disagreed.

“That wasn’t a hit,” Radford whispered, watching as Martinez stomped off. “It tapped him lightly.”

Others cheered the transit system’s efforts.

“I like these,” said Castro Valley resident Mark Murphy, noting that the stacked gates, however unwelcoming, aim to stop two common types of fare evasion. They’re too tall for people to vault over, and they close with extra air pressure so would-be scofflaws can’t pry them open.

“It’s like pushing down on a parking brake,” Radford said.

Sylvie Sather also praised the new gates. A resident of Point Richmond, she passed through rolling a suitcase on Friday.

“I think all of you were more nervous for me than I was for myself,” Sather said, gesturing at Allen and the other staff.

BART began tackling fare cheating in 2017, when its board of directors passed an ordinance empowering the agency to hand out citations to any rider who couldn’t show proof-of-payment. Since then, managers and board directors have toyed with the idea of replacing all 600 gates, which could cost $150 million to $200 million and change the open, roomy feel of the stations.

Engineers are toiling away in a laboratory on the second floor of BART’s Oakland headquarters, making alterations to “harden” the orange consoles without completely overhauling them. In addition to the model on display in Richmond, they’re testing another cinched design at Embarcadero that closely resembles the original gates, except that the wedges closer tighter. Soon the agency will debut a “pop-up” barrier at Fruitvale, with plates that jut out as soon as the gates close.

Officials estimate it would cost $15 million to $20 million to modify gates throughout the system, far less expensive than a total replacement — which some board directors still favor. In May, the directors looked at four options for new gates, ranging from a slightly altered version of the current pie wedges, to the prison-style bars of the New York subway.

The agency probably will stick with the same template and keep adding new fixtures: extra air pressure, pop-up plates, barriers stacked one atop the others, maybe sloped tops that are harder to vault over.

“The thing is, we had to roll out something urgently, using existing pieces that would be inexpensive and easy to test,” said board Director Janice Li. She’s urged BART to invest in tall gates and other barricades, rather than hiring fare inspectors who might single out people they perceive as criminals.

Even so, Li chides BART management for not adequately preparing riders before they put the gates in. Within days of the rollout, a “guillotine” meme had spread on social media.

“Yes, right now, some of this stuff is going to look like it came out of Frankenstein’s lab,” board President Bevan Dufty said. He insisted the new gates are safe and that comparisons to French beheading devices “are not helpful.”

“We’re not going for aesthetics,” he said. “We’re going for practicality.”

Rachel Swan is a San Francisco Chronicle staff writer. Email: rswan@sfchronicle.com Twitter: @rachelswan