(Reuters) -The National Highway Traffic Safety Administration said Wednesday it has certified Amazon.com's self-driving unit Zoox vehicles for demonstration use and closed a probe into whether they had complied with federal requirements.

The U.S. auto safety agency in 2022 began a probe into whether the self-driving vehicles lacking traditional driving controls had met federal safety requirements when the company self-certified the vehicle.

Zoox in June applied for an exemption from some requirements and NHTSA granted it, saying all of purpose-built vehicles manufactured by Zoox now operating on public roads in the United States are doing so pursuant to an exemption issued by the agency.

The Trump administration in June said it would move faster on self-driving exemption requests to deploy up to 2,500 self-driving vehicles after prior proposals from General Motors and Ford to deploy vehicles without steering wheels and brake pedals lingered for years and were eventually withdrawn.

NHTSA's approval includes the requirement Zoox remove all existing statements that the purpose-built vehicle complies with applicable federal motor vehicle standards.

In May, Zoox agreed to recall 270 driverless vehicles after an unoccupied robotaxi was involved in an April 8 crash with a passenger car in Las Vegas.

The Zoox Automated Driving Systems in certain driving scenarios "may make an inaccurate prediction when another vehicle slowly approaches perpendicularly and stops. In these scenarios, the Zoox vehicle may not be able to avoid a crash."

Zoox paused operations for several days pending a safety review of the incident and developed a software update to address the issue.

In April, the NHTSA closed a probe into 258 Zoox vehicles over a braking issue after Zoox issued a recall to update their software. It opened the probe in May 2024 following two rear-end collisions that injured motorcyclists after the automated vehicles braked unexpectedly.