WASHINGTON (Reuters) - The National Highway Traffic Safety Administration said Wednesday it is seeking additional details about a series incidents that raise concerns about the performance of Alphabet's Waymo self-driving vehicles.

In May, the U.S. auto safety regulator opened an investigation after 22 reports of its robotaxis exhibiting driving behavior that potentially violated traffic safety laws, or demonstrating other "unexpected behavior," including 17 collisions.

The agency on Wednesday said Waymo is to respond to a series of detailed questions by Aug 6 including comprehensive details of all travel on public roads by the company's driverless vehicles.