(Reuters) -Tesla reached out to Arizona late last month to start a certification process for an autonomous vehicle ride-sharing service, and a decision is expected by the end of this month, the state's transportation department said on Thursday.

"They have expressed interest in operating within the Phoenix Metro area," Arizona's Department of Transportation said in an email to Reuters. Tesla has applied to test and operate both with and without a driver, it said.

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

Even as social media videos showed multiple traffic problems and driving issues over the first few days, CEO Elon Musk said on Wednesday that Tesla would expand the service to a larger area in the city this weekend and, depending on regulatory approvals, to the San Francisco Bay Area within two months.