Waymo is recalling thousands of its self-driving cars in the US over a software issue that could allow vehicles to drive into flooded roads. According to a letter posted on the National Highway Traffic Safety Administration (NHTSA) website on Tuesday, the voluntary recall affects nearly 3,800 robotaxis that use the company's fifth and sixth-generation automated driving systems. It follows an incident on 20 April in San Antonio, Texas, where an empty Waymo vehicle entered a flooded road and was swept into a creek. The company, which hopes to be operating a robotaxi service in London by September, said it was working on additional software safeguards, according to CNBC. The BBC has contacted Waymo, which is owned by Google's parent company Alphabet, for comment.