WASHINGTON (Reuters) - The U.S. auto safety agency disclosed on Thursday it has opened 27 investigations into crashes of Tesla vehicles, 23 of which remain active, and at least three of the crashes occurred in recent weeks. The National Highway Traffic Safety Administration (NHTSA) confirmed Thursday that it will send a team to investigate a recent Tesla crash in the Houston area. Four of the 27 NHTSA investigations have been completed and the results published. Earlier this week, NHTSA said it was sending its special crash investigation team to probe two crashes in Michigan, including a crash early Wednesday involving a Tesla suspected of being in Autopilot mode when it struck a parked Michigan State Police patrol car. Tesla did not immediately comment. NHTSA said in July that its “(Special Crash Investigations team) has looked into 19 crashes involving Tesla vehicles where it was believed some form of advanced driver assistance system was engaged at the time of the incident.” Michigan State Police said a parked patrol car was struck by a Tesla apparently in Autopilot mode while investigating a traffic crash near Lansing on Interstate-96. No one was injured and the 22-year-old Tesla driver was issued traffic citations. On Monday, NHTSA said it was sending another team to investigate a “violent” March 11 crash in Detroit in which a Tesla became wedged underneath a tractor-trailer and left a passenger in critical condition. Detroit police said Tuesday they do not believe that Autopilot was in use. The Autopilot feature was operating in at least three Tesla vehicles involved in fatal U.S. crashes since 2016. Tesla advises drivers they must keep their hands on the steering wheel and pay attention while using Autopilot. However, some Tesla drivers say they are able to avoid putting their hands on the wheel for extended periods when using Autopilot. NHTSA’s Special Crash Investigation team typically looks at more than 100 crashes a year with a focus on emerging technologies. Issues in recent years include performance of alternative fueled vehicles, child restraint systems, adaptive controls, safety belts, vehicle-pedestrian interactions, and potential safety defects. Separately, the agency said it had been briefed on Tesla’s “full self-driving” (FSD) software. Tesla Chief Executive Elon Musk wrote on Twitter last week that the beta FSD software had been expanded to about 2,000 owners while other drivers had access to the program revoked. The agency said it “will monitor the new technology closely and will not hesitate to take action to protect the public against risks to safety.” NHTSA said the system does not make the Tesla “capable of driving itself. The most advanced vehicle technologies available for purchase today provide driver assistance and require a fully attentive human driver at all times performing the driving task and monitoring the surrounding environment.”