The top U.S. auto-safety regulator opened an investigation into Waymo, the autonomous-vehicle subsidiary of subsidiary of Alphabet Inc., after 22 incidents in which the company’s cars were involved in collisions or may have violated traffic laws.

The U.S. National Highway Traffic Safety Administration’s Office of Defect Investigation opened a preliminary evaluation after receiving reports that Waymo vehicles crashed into objects including gates, chains and parked cars. The agency also cites instances in which the company’s automated-driving system appeared to disobey traffic-control devices.

NHTSA said its initial reviews indicated that Waymo’s system either was engaged throughout the incidents, or was disengaged in the moments just before they occurred by an in-vehicle test driver. The probe covers an estimated 444 vehicles, according to documents posted on the agency’s website Tuesday.

Waymo said in a statement it is “proud of our performance and safety record over tens of millions of autonomous miles driven, as well as our demonstrated commitment to safety transparency.” The company vowed to work with NHTSA as it conducts the latest probe. 

NHTSA has been subjecting both driver-assistance systems and more advanced autonomous vehicles to greater scrutiny. It’s launched probes of Tesla Inc.’s Autopilot, Ford Motor Co. BlueCruise and Amazon.com Inc.’s Zoox since last month. NHTSA also opened an investigation of possible defects in the automated-driving system developed by General Motors Co.’s self-driving unit Cruise in October.