WASHINGTON : U.S. auto safety investigators asked Tesla to answer questions on its plans to launch a paid robotaxi service in Austin, Texas, in June, in order to assess how the electric vehicle maker's cars with full self-driving technology will perform in poor weather. The National Highway Traffic Safety Administration, in a letter made public on Monday, said it has been investigating Tesla full self-driving collisions in reduced roadway visibility conditions since October. NHTSA said it is