The automated driving software at the heart of Waymo, a robotaxi startup owned by Alphabet, Google’s parent company, is now under investigation by a U.S. federal agency.

The National Highway Traffic Safety Administration opened a preliminary evaluation of about 444 Waymo autonomous vehicles on Tuesday after receiving 22 reports of Waymo’s robotaxis behaving unexpectedly.

The reports detailed that some of Waymo’s self-driving cars seemed to drive in opposing lanes, enter construction zones, and ignore traffic safety rules. In certain cases, they collided with parked vehicles or objects like gates.

The filing did not record any injuries or fatalities resulting from these collisions.

The NHTSA received news of collision incidences from Waymo and counted others from publicly available reports.

The agency will now evaluate how well Waymo’s automated driving system picks up on traffic control devices, responds to them, and avoids contact with other vehicles.

Related: Traffic Jam Caused by Self-Driving Cars in San Francisco Sparks Outcry and Safety Concerns

Waymo publicly touted its most recent numbers recently: 50,000 paid trips carried out weekly and over a million rider-only trips in total.

Waymo maintains that its robotaxis are significantly safer than human-driven vehicles, and has released research reports supporting its claims.

The Waymo probe is the second robotaxi investigation the NHTSA has announced in two days. It’s the fourth self-driving technology inquiry from the agency in less than a month.

The NHTSA publicly opened an investigation into Amazon-backed Zoox on Monday after its self-driving cars braked suddenly two separate times, causing rear-end collisions.

Related: Waymo’s Driverless Robotaxi Fleet Is Making 50,000 Trips Per Week

In April, the NHTSA said it was investigating Ford’s BlueCruise driver assistance after two Mustang Mach-E cars outfitted with the technology collided with stationary cars.

The agency is also looking into Tesla’s Autopilot technology, which has been tied to over 200 crashes and 29 fatalities.

Tesla will soon enter the robotaxi market: CEO Elon Musk wrote that the Tesla Robotaxi unveil will happen on August 8.

Related: Elon Musk Reveals When Tesla Will Release Its First Robotaxi

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