(Reuters) -Tesla tiptoed into its long-awaited robotaxi service in Austin, Texas on Sunday with about 10 of its Model Y SUVs that will operate within strict limits. 

The rides were being offered on Sunday for a flat fee of $4.20, CEO Elon Musk said in an X post, and social media influencers were seen booking and taking rides in the robotaxis in several Austin locations, according to videos reposted by Musk.

Musk has said the company is being "super paranoid" about safety and that humans will remotely monitor the fleet, which also have safety monitors in front passenger seats.

Remote access and control - known in the industry as "teleoperation" - is used in varying degrees by the handful of robotaxi startups operating around the globe. The technology has clear advantages and important limitations.  

Here are some details of how it works:

WHAT IS TELEOPERATION?

Teleoperation is the control of machines by humans in a different location, usually over a wireless network.

It is used to train robots to operate autonomously, monitor their autonomous activity, and take over when required.    

HOW DO ROBOTAXI OPERATORS USE TELEOPERATION?

The global robotaxi industry is still in test mode, as companies deploy the vehicles in limited geographic areas and continually adjust the artificial intelligence software that controls them. Teleoperation is often used to intervene when a vehicle is unsure of what to do. 

Alphabet's Waymo, for example, has a team of human "fleet response" agents who respond to questions from the Waymo Driver - its bot.

"Much like phone-a-friend, when the Waymo vehicle encounters a particular situation on the road, the autonomous driver can reach out to a human fleet response agent for additional information," Waymo said in a blog post last year.

Former Waymo CEO John Krafcik told Reuters, "the cars aren't being actively monitored," adding that the software is "the ultimate decision-maker." 

A Waymo video shows a car asking a remote operator whether a street with emergency response vehicles is open to traffic. When the human says yes, the vehicle proceeds.

In contrast, other companies, such as Baidu's Apollo Go in China, have used fully remote backup drivers who can step in to virtually drive the vehicles. Baidu declined to comment.

WHAT ARE THE LIMITATIONS?

Driving vehicles remotely on public roads has a major potential problem: it relies on cellular data connections that can drop or operate with a lag, disconnecting the vehicle from the remote driver in dangerous situations.

Philip Koopman, a Carnegie Mellon University engineering professor and autonomous-vehicle safety expert, said that approach could work for a small test deployment of 10 vehicles, such as Tesla's initial effort in Austin, but he called teleoperation "inherently unreliable technology."

"Eventually you will lose connection at exactly the worst time," he said. "If they've done their homework, this won't ever happen for 10 cars. With a million cars, it's going to happen every day." 

Former Waymo CEO Krafcik agreed, adding that the time delay in cell signal makes remote driving "very risky."

On the other hand, relying on the vehicle to reach out for help and allowing the vehicle to be the decision-maker are risky as well, Koopman said, as it does not guarantee the vehicle will make the right decision.

Waymo declined to comment on the limitations of its approach.

Koopman also noted there are limits to how many vehicles one person can safely monitor.

A group of Democratic Texas lawmakers had asked Tesla on Wednesday to delay its robotaxi launch until September, when a new autonomous-driving law is scheduled to take effect. The Austin-area lawmakers said in a letter that delaying the launch "is in the best interest of both public safety and building public trust in Tesla's operations."

WHAT IS TESLA'S APPROACH?

Musk for years has promised, without delivering, that its Full Self-Driving (Supervised) advanced driver assistance software would graduate to completely self-driving and control robotaxis. This year, he said Tesla would roll out a paid service in Austin underpinned by an "unsupervised" version of the software.

"Teslas will be in the wild, with no one in them, in June, in Austin," Musk told analysts and investors in January. In May, he told CNBC that the robotaxi would only operate in parts of Austin that are safe for it, would avoid difficult intersections, and would use humans to monitor the vehicles.

What those teleoperators are doing is not clear. 

For years inside Tesla, company executives have expected to use teleoperators who could take over in case of trouble, said one person familiar with the matter. For instance, if a robotaxi were stuck in a crowded pedestrian area and confused about what to do next, a human teleoperator could take over and guide it, the source said.

Tesla advertised for teleoperation positions, saying the company needs the ability to "access and control" autonomous vehicles and humanoid robots remotely. Such employees can "remotely perform complex and intricate tasks," it said in the advertisements.

Tesla did not respond to a request for comment. 

"We are being super paranoid about safety," Musk said in a post ahead of the launch.