The U.S. National Highway Traffic Safety Administration (NHTSA) has opened a preliminary investigation into Waymo’s self-driving vehicles after one was reported to have driven around a stopped school bus in Atlanta, Georgia.

The incident, which occurred on 22 September, involved a fifth-generation Waymo automated vehicle that passed the bus while its red lights, stop arm, and crossing control arm were deployed, as students were disembarking. No injuries or crashes were reported.

According to NHTSA, the vehicle, operating without a human safety driver, initially stopped before manoeuvring around the front of the bus and continuing down the road.

The agency said the investigation will assess how Waymo’s autonomous driving system complies with school bus traffic laws and whether similar incidents have occurred.

Waymo’s autonomous fleet surpassed 100 million miles of driving earlier this year and currently adds around two million miles per week.

According to a Waymo spokesperson, the company is aware of the investigation and has already made updates to improve the robotaxi’s performance and plans to implement more.

They added that the bus was partially blocking a driveway that the Waymo car was exiting, and that the lights and stop sign were not visible from the taxi’s point of view.