Earlier this week, Amazon’s autonomous tech company Zoox announced it deployed the world’s first purpose-built robotaxi on open public roads with passengers.

Zoox said it conducted the first run of its employee shuttle service in Foster City, California on February 11, marking the first time in history a purpose-built autonomous robotaxi without traditional driving controls carried passengers on open public roads.

Unlike a conventional car and the vehicles most other robotaxi developers are using, the Zoox fully autonomous vehicle lacks a steering wheel, brake pedal and other controls human drivers need.

The company said it completed rigorous testing on private roads to reach this milestone and received approval from the California Department of Motor Vehicles (DMV) to operate its robotaxi on the state’s public roads.

More specifically, to obtain the permit, Zoox self-certified that the electric vehicle met existing Federal Motor Vehicle Safety Standards (FMVSS). To date, Zoox is the only purpose-built robotaxi to take the self-certification route.

While manufacturers can self-certify compliance, the National Highway Traffic Safety Administration (NHTSA) may scrutinize self-certifications in some cases to ensure they conform with the standards.

That’s exactly what’s happening now with Zoox, as Automotive News reports. “The agency is evaluating the basis for these self-certification claims and, as part of this effort, continues to review information provided by Zoox in response to questions previously posed by the agency,” a NHTSA spokesperson told the publication.

Federal regulators are now reviewing whether the robotaxi made by Zoox meets requirements to travel on public roads. The NHTSA does not pre-approve or prohibit the introduction of new vehicles or vehicle tech, so long as they conform with the motor vehicle safety standards.

Autonomous vehicles that do not comply with the standards can still be deployed provided that the companies first receive a NHTSA exemption. Zoox did not apply for an exemption – such as GM for its Cruise Origin robotaxi – or pursue other regulatory avenues. Despite that, Zoox CEO Aicha Evans said there were “no limitations” on the company’s deployment.

The company claims its robotaxi incorporated FMVSS performance requirements directly into its vehicle and added “more than 100 safety innovations not available in today’s passenger cars.” Zoox does not elaborate on how it interpreted the federal standards and its compliance, though.

But many autonomous vehicle experts are wondering, Automotive News points out. The publication cites Sam Abuelsamid, principal analyst at consulting firm Guidehouse Insights, who warned there is “some potential risk in this.” He also said “it is still an open question on whether what Zoox is doing is legit,” even though their legal team “seems to think it is.”

For now, Zoox uses a single robotaxi traveling a 1-mile (1.6-km) public route between the company’s two main office buildings carrying up to four people at a time at up to 35 mph (56 km/h). Zoox says it is capable of handling left-hand and right-hand turns, bi-directional turns, traffic lights, cyclists, pedestrians, vehicles, and other road agents on this route. 

The employee shuttle service will be offered exclusively to all Zoox full-time employees, but the Amazon-owned company plans to offer robotaxi rides to the general public after it secures additional government clearances.