On an undisclosed Bay Area freeway over the past couple of weeks, a camera system has been counting the people inside every vehicle in the carpool lane in an experiment to detect cheaters.

No tickets or warnings are being issued, but that could change if Bay Area transportation officials are convinced that the technology is the next-generation enforcement answer to a growing number of scofflaws who, despite the risk of a heavy fine, use the region’s restricted carpool lanes to shave time off their commute.

Studies by regional transportation agencies and The Chronicle have found that Bay Area carpool lanes reserved for vehicles with two or more occupants — three or more on Interstate 80 — and clean-energy cars are commonly crowded with solo drivers who have no business being there. Tickets run $490.

In recent months, the California Highway Patrol has increased enforcement, assigning dedicated strike teams working overtime shifts to catch the cheats, but the agency has been unable to abate the problem. Lanes created to move at a decent clip are sometimes as sluggish as the regular lanes, triggering rising frustration in drivers legitimately using the carpool lane and in those stuck in the slower lanes watching cheaters pass them by.

“If the system breaks down because there’s no trust in the system and everyone’s cheating, that’s a problem. I don’t think we can just sit by and do nothing,” said Randy Rentschler, a spokesman for the Metropolitan Transportation Commission, which oversees carpool-lane operations for the Bay Area.

The camera technology being tested comes from one of three firms with systems that MTC has decided to look at. All three claim their automated systems can snap photos of a passing vehicle, accurately count the number of passengers and send citations to violators. All three will be tested in turn. The MTC will review the results for reliability and effectiveness sometime this summer.

“The goal here is to demonstrate that (the technology) ... can work with a high degree of accuracy,” Rentschler said.

Even if the technology proves effective, it could still be a long road to employing the system on Bay Area freeways. The MTC would need state legislation allowing passenger-counting cameras to be used to issue citations. And they’d have to overcome privacy concerns about cameras peering into vehicles, reading license plates and keeping records of the numbers of occupants.

But first, Rentschler said, “We can’t even have the political discussions until we prove that we can do it.”

Drivers interviewed last week at a Berkeley gas station near Interstate 80, which has the Bay Area’s busiest carpool lanes, agreed with the need for better enforcement, but some were leery.

Emma Em, 40, a singing teacher, thought the idea sounded intrusive.

“It feels like an invasion of privacy,” she said, “but I hate the cheaters.”

Nate Cope, 29, a Berkeley data analyst, was more upbeat.

“It sounds like a good idea,” he said. “It makes it fair. I definitely see a lot of people in the carpool lane by themselves.”

The three companies MTC has contracted with for the tests are Conduent (formerly Xerox), Transcor and Indra. The systems will be tested along the same stretch of freeway in consecutive months. Rentschler said all the companies boast accuracy rates greater than 95 percent in use elsewhere.

The systems employ a variety of tools to enable them to look inside vehicles, even through dark-tinted windshields, to count passengers. They include standard and infrared cameras that can detect human skin, systems that illuminate images to make them easier to read and geometric algorithms.

MTC officials won’t reveal the site of the tests for fear of vandalism or theft of equipment and concern that cheaters might change their behavior if they’re aware they’re being watched. Just as no citations based on the testing are being issued, no license-plate data are being recorded, either, Rentschler said.

The San Diego Association of Governments, MTC’s equivalent in San Diego County, conducted a similar test over 30 days in 2015 with Conduent, then known as Xerox State and Local Solutions, on the Interstate 15 express lanes.

“The results were mixed and inconclusive,” said Jessica Gonzales, a spokeswoman for the San Diego agency. She said the association hasn’t pursued the use of the cameras but is monitoring the advancement of the technology, including tests like the one under way in the Bay Area.

California law limits the use of automated cameras to issuing tickets to red-light runners and toll evaders, so legislation would be required to expand camera use to passenger counts. Legislators, however, have been reluctant to expand camera enforcement, particularly for speeding violations, something San Francisco has sought in recent years.

To sell legislators on the idea for carpool lanes, transportation officials will have to show not only that the cameras can count the occupants accurately, but that they can differentiate a dog or a well-dressed dummy from a human passenger, as well as detecting a sleeping infant in a rear-facing carrier in the back seat, Rentschler said.

Dave Maass, senior investigative researcher for the Electronic Frontier Foundation, a San Francisco nonprofit that aims to protect civil liberties in the digital age, said the occupant-counting technology raises questions about privacy, including how the information is used, whether it’s recorded and saved, and what else the cameras allow the government to see inside a vehicle.

“This is getting into a whole new creepy area,” Maass said. “If we are getting to a point where they are beaming stuff into your car, that raises a whole new range of civil liberties issues.”

The CHP, the agency now tasked with carpool, or high-occupancy, lane enforcement, does it the old-fashioned way, looking into vehicles and pulling over drivers they suspect of cheating. But it’s difficult for an officer to accurately and quickly count occupants, and there’s frequently no safe place on freeways to pull drivers over.

“There are always going to be factors that make it hard to enforce HOV (high-occupancy vehicle) lanes,” said Sgt. Rob Nacke, a Bay Area CHP spokesman, “but we want to make sure our officers are visible out there.”

The CHP has not staked out an official position on occupant-counting cameras, said spokeswoman Fran Clader. But drivers have told the agency, via customer surveys and social media, that they want greater enforcement of the lanes. State Sen. Jerry Hill, D-San Mateo, has introduced legislation to provide additional resources to the task, including authorizing new approaches.

Whether the public’s frustration with carpool lane cheaters can outweigh privacy concerns and the creepy feeling of being spied on may determine the future of passenger-counting cameras in the Bay Area.

“It’s good and it’s bad,” said Mack Moaven, 53, a commuter who lives in San Francisco. “Good because it stops violators, but bad because it violates the privacy of people. They’re going to start with your car, and they’ll be checking your house before long. The government wants to know what you’re doing.”

Rentschler acknowledged the Bay Area’s unease with cameras as well as its intolerance for carpool-lane cheaters. The issue, he said, will become even more important as the region expands its network of carpool and combined carpool-toll express lanes to 550 miles by 2035.

“The choice,” he said, “is underperforming carpool lanes — or this.”