(Reuters) - Tesla has been approved to start testing autonomous robotaxi vehicles with a safety monitor in Arizona, the state transportation department said in an email to Reuters on Friday.

Tesla had applied in June for a permit to begin trials for an autonomous vehicle ride-sharing service, and now plans to test robotaxis in the Phoenix Metro area using safety drivers, the Arizona Department of Transportation said in its email.

Tesla did not respond to a Reuters request for comment. It was not immediately clear when the trials would start or how long they would last.

Tesla Chief Executive Elon Musk previously stated that Tesla plans to launch an autonomous ride-hailing service to about half of the U.S. population by the end of this year.

Tesla rolled out a small test of its robotaxi service in a limited area of Austin, Texas, in June, with about a dozen vehicles, a select group of passengers and many restrictions, including a safety monitor in the front passenger seat.