(Reuters) -The U.S. National Highway Traffic Safety Administration (NHTSA) said on Monday it has opened an investigation into about 2,000 Waymo self-driving vehicles after reports the robotaxis behaved unsafely near stopped school buses.

NHTSA said, citing a media report, that in one incident a robotaxi initially stopped beside a school bus then drove around its front, passing the extended stop arm and crossing control arm as students were disembarking.

Waymo did not immediately respond to a Reuters request for comment.