DETROIT – Three times in the past four months, William Stein, a technology analyst at Truist Securities, has accepted Elon Musk’s invitation to try out the latest versions of Tesla’s vaunted “Full Self-Driving” system.

A Tesla equipped with this technology, the company said, could drive from place to place with little human intervention. But every time Stein drove one of the cars, the vehicle performed unsafe or illegal maneuvers, he said. His last test drive earlier this month, Stein said, “frightened” his 16-year-old son, who was accompanying him.

Stein’s experience, as well as a Tesla crash in the Seattle area in April that killed a motorcyclist, have drawn the attention of federal authorities, who have been investigating Tesla’s automated driving systems for more than two years because dozens of crashes have raised safety concerns.

The problems have caused people who observe autonomous vehicles to become more skeptical that Tesla’s automated system will ever be able to operate safely at scale. Stein says he doubts Tesla is anywhere close to being able to deploy a fleet of autonomous robotaxis next year, as Musk has predicted.

The latest incidents come at a crucial time for Tesla. Musk has told investors that it is possible that autonomous vehicles will be able to drive more safely than human drivers by next year or even by the end of this year.

And in less than two months, the company is set to unveil a vehicle built specifically as a robotaxis. For Tesla to put robotaxis on the road, the company must show regulators that the system can drive more safely than humans, Musk said. Federal regulations require Teslas to meet national vehicle safety standards.

Musk has released data showing miles driven per accident, but only for Tesla’s less sophisticated Autopilot system.

Safety experts say the data is invalid because it only counts serious crashes in which airbags were deployed and does not show how often human drivers had to take control to avoid a collision.

Fully autonomous driving is currently used by around 500,000 Tesla owners on public roads – just over one in five Teslas in use today. Most of them have paid $8,000 or more for the optional system.

The company points out that vehicles equipped with this system cannot drive themselves and that drivers must be ready to intervene at all times if necessary.

Tesla also says it tracks each driver’s behavior and will remove their ability to drive fully autonomously if they don’t properly supervise the system. Recently, the company started calling the system fully autonomous driving (supervised).

Musk has acknowledged that his previous predictions about the deployment of autonomous driving were too optimistic, and in 2019 promised a fleet of autonomous vehicles by the end of 2020.

Five years later, many who follow the technology say they doubt it will work as promised across the United States.

“That’s not even close to happening and it won’t happen next year,” said Michael Brooks, executive director of the Center for Auto Safety.

The car Stein was driving was a Tesla Model 3, which he picked up at a Tesla showroom in Westchester County, north of New York City.

The car, Tesla’s most affordable vehicle, was equipped with the latest software for fully autonomous driving. Musk says the software now uses artificial intelligence to control the steering and pedals.

During his drive, Stein said, the Tesla felt smoother and more human than previous models. But on a trip of less than 10 miles, the car turned left through a red light.

“It was breathtaking,” said Stein.

He said he did not take over the car because there was little traffic and the maneuver did not seem dangerous to him at the time.

Later, however, the car drove down the middle of an avenue, spanning two lanes heading in the same direction.

This time, Stein said, he intervened.

The latest version of fully autonomous driving, Stein wrote to investors, “does not solve the problem of autonomy” as Musk predicted. And it “doesn’t seem to match the capabilities of robotaxis.” During two previous test drives in April and July, Stein said, Tesla vehicles also surprised him with unsafe maneuvers.

Tesla did not respond to messages seeking comment.

Stein said that while he believes Tesla will eventually make money with its driving technology, he does not see a robotaxi without a driver and with a passenger in the back seat in the near future.

He predicted that there would be significant delays and that transportation options would be limited.

Stein pointed out that there is often a significant gap between what Musk says and what is likely to happen.

Many Tesla fans have posted videos on social media showing their cars driving autonomously without a human taking control.

Videos, of course, do not show how the system behaves over time. Others have posted videos showing dangerous behavior.

Alain Kornhauser, director of autonomous vehicle studies at Princeton University, said he drove a Tesla borrowed from a friend for two weeks and found that the car consistently recognized pedestrians and other drivers.

Although the car runs well most of the time, Kornhauser said he had to take control when the Tesla made movements that frightened him.

He warns that fully autonomous driving is not yet at the point where it can operate everywhere without human supervision.

“This thing,” he said, “is not at a point where it can go anywhere yet.”

Kornhauser is convinced that the system could function autonomously in smaller areas of a city, where detailed maps help orient the vehicles.

He wonders why Musk doesn’t start offering rides on a smaller scale.

“People could really use the mobility this would provide,” he said.