DETROIT (AP) — The U.S. government’s highway safety agency has opened another investigation of automated driving systems, this time into crashes involving Waymo’s self-driving vehicles.

The National Highway Traffic Safety Administration posted documents detailing the probe on its website early Tuesday after getting 22 reports of Waymo vehicles either crashing or doing something that may have violated traffic laws.

In the past month, the agency has opened at least four investigations of vehicles that can either drive themselves or take on at least some driving functions as it appears to be getting more aggressive in regulating the devices.

In the probe of Waymo, which was once Google’s self-driving vehicle unit, the agency said it has reports of 17 crashes and five other reports of possible traffic law violations. No injuries were reported.