Federal safety regulators are once again looking into Tesla's self-driving mode, the latest in a seemingly endless stream of investigations into the safety of the technology.

Last week, the National Highway Traffic Safety Administration announced at least the sixth investigation into Tesla vehicles using the company's "Full Self Driving" (FSD), or other driver assist features. This probe covers dozens of dangerous driving incidents, including blowing through red lights, driving in the wrong lane of traffic, and three accidents that resulted in five injuries.

But there's relatively little NHTSA, or any federal regulator, can do to regulate the new features Tesla introduces amid its ambitious plans to fill the country with self-driving cars and "robotaxis."

That's because it's not a regulator's job to approve the technology - only to rein it in if it causes problems. American laws aren't equipped to deal with the fast-moving ambitions of CEO Elon Musk, and Washington doesn't seem in a hurry to regulate his company.

A Tesla model Y and other Telsla vehicles sit at a dealership in Georgia, in March.

Mike Stewart/AP

NHTSA already had several probes into Tesla's self-driving tech, including into incidents that resulted in fatal crashes, for both its FSD and less advanced driver assistance feature called "Autopilot." But many of those investigations began years ago and are still ongoing, even as more and more Teslas with FSD and Autopilot hit American roads.

"I call it regulatory whack-a-mole," said Bryant Walker Smith, a professor of law and engineering and an affiliated scholar at the Center for Internet and Society at Stanford Law School. "This process takes a very long time. This is the first step in multiple steps required for an actual recall. It's a regulatory process that isn't necessarily well aligned with the technological time frame."

'Real-world guinea pigs'

Tesla is not unique. Despite what most drivers might believe about the safety of the new cars they buy, much of the regulation actually takes place after cars are already on the road.

The United States has what's known as a self-certification regime. NHTSA creates specific standards and automakers then self-certify, or "promise that their vehicles or systems comply with those specific standards," Smith said.

But "if there's not a standard specific to a given technology, then there's nothing to self-certify. And NHTSA does not have specific standards for the performance of many advanced driver assistance systems," he said.

But Smith added that problem is not simply cars with driver assistance features, but with all cars on the road.

"We are all real-world guinea pigs in the century long experiment introducing two-ton vehicles that travel at speed faster than we can comprehend," he said.

Cars make their way heading east out of Los Angeles during the evening rush hour on January 25, 2024.

Frederic J. Brown/AFP/Getty Images

Limits to what safety regulator can do

NHTSA could set higher safety standards for vehicles, Smith said. But its ability to test vehicles and features before they are allowed on the road is limited by law and regulation.

To give the agency the authority to approve or reject a new vehicle or feature before it is introduced into service, like the Federal Aviation Administration does with commercial aircraft, would require Congress to change the law.

Smith said that change isn't going to be made any time soon. Besides the power of the auto industry, Americans have become accepting of the ten of thousands of car crash fatalities every year.

He said they are more likely to blame the drivers than demand greater regulation.

"That kind of approval applies to scary things, like nuclear power plants and planes and haircuts and initial stock offerings," he said.

Tesla's growing self-driving ambitions

Musk is betting the future of Tesla on technology like self-driving. But despite names like "full self-driving" and "autopilot," the company admits that owners using those features need to be behind the wheel, ready to take over.

But Tesla is beginning to plans to offer true driverless driving without anyone behind the wheel.

A vehicle Tesla is using for robotaxi testing purposes in Austin, Texas.

Eli Hartman/Bloomberg/Getty Images

The company launched its long-promised robotaxi service in Austin, Texas, earlier this year, although after starting with a Tesla employee in the front passenger seat, local regulators required the employee move to the driver's seat. But Musk also promises the service will soon have no employees behind the wheel, as well as a true self-driving "Cybercab" with no brake, accelerator or steering wheel.

Tesla did not respond to CNN's request for comment. The company has insisted that its cars using self-driving technology are safer than human drivers.

Safety experts, however, said that Tesla has not produced the data needed to prove that claim. And even a driver sitting behind the wheel of a car using FSD poses a risk.

"There's great, great concern that humans, simply as a matter of psychology and physiology, are going to lose attention if they are doing nothing but watching, while their cars are doing everything else," Smith said.

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