Waymo said on Tuesday it is recalling about 3,800 robotaxis in the United States after identifying a risk that vehicles could enter flooded roads with higher speed limits, raising safety concerns.

The Alphabet unit said the recall followed an incident on April 20 when a Waymo vehicle drove into a flooded lane in San Antonio during extreme weather. Waymo said the vehicle was unoccupied, and there were no injuries, but the incident prompted the company to review similar scenarios involving high speeds and impassable flooded roads.

“We are working to implement additional software safeguards and have put mitigations in place, including refining our extreme weather operations during periods of intense rain, limiting access to areas where flash flooding might occur,” Waymo said.

The National Highway Traffic Safety Administration said Waymo has temporarily narrowed its operating scope to increase weather-related restrictions and updated its maps while it works on a permanent remedy.

Separately, Waymo is facing an NHTSA investigation after one of its self-driving vehicles struck a child near an elementary school in Santa Monica, California, in January, causing minor injuries.

In March, the National Transportation Safety Board said it was investigating a January incident in which Waymo self-driving vehicles passed a stopped school bus with its lights activated in violation of Texas state law.

(Reporting by David Shepardson in Washington and Ananya Palyekar in Bengaluru. Editing by Janane Venkatraman and Mark Potter)