The US’s federal transportation regulator said Thursday it had opened an investigation after a Waymo self-driving vehicle struck a child near an elementary school in southern California last week, causing minor injuries.

The National Highway Traffic Safety Administration said the child in Santa Monica ran across the street on 23 January from behind a double parked SUV towards the school and was struck by the Waymo autonomous vehicle during normal school drop-off hours. The agency said there were other children, a crossing guard, and several double-parked vehicles in the vicinity.

The federal agency is opening a preliminary evaluation to investigate whether the Waymo AV exercised appropriate caution given its proximity to the elementary school during drop-off hours, and the presence of young pedestrians and other potential vulnerable road users. The agency said it plans to examine the vehicle’s “intended behavior in school zones and neighboring areas, especially during normal school pick up/drop off times, including but not limited to its adherence to posted speed limits” and will “also investigate Waymo’s post-impact response”.

Waymo said in a post on its blog: “The Waymo Driver braked hard, reducing speed from approximately 17 mph to under 6 mph before contact was made.”

“To put this in perspective, our peer-reviewed model shows that a fully attentive human driver in this same situation would have made contact with the pedestrian at approximately 14 mph,” the post reads. According to Waymo, the child stood up and walked to the sidewalk. The autonomous car moved to the side of the road.

The US transportation regulator has also opened an investigation into how Waymo vehicles approach school buses. Multiple schools reported incidents of the autonomous vehicles failing to stop or fully slow down as children were being dropped off.