DETROIT — The U.S. government has opened a formal investigation into Tesla’s Autopilot partially automated driving system, saying it has trouble spotting parked emergency vehicles.

The National Highway Traffic Safety Administration announced the action today in a posting on its website.

The agency says it has identified 11 crashes since 2018 in which Teslas on Autopilot or Traffic Aware Cruise Control have hit vehicles with flashing lights, flares, an illuminated arrow board or cones warning of hazards.

The investigation covers the Models Y, X, S and 3 from the 2014 through 2021 model years.

Autopilot has frequently been misused by Tesla drivers, who have been caught driving drunk or even riding in the back seat while a car rolled down a California highway.

The agency has sent investigative teams to 31 crashes involving partially automated driver assist systems since June of 2016. Such systems can keep a vehicle centered in its lane and a safe distance from vehicles in front of it. Of those crashes, 25 involved Tesla Autopilot in which 10 deaths were reported, according to data released by the agency.

Tesla and other manufacturers warn that drivers using the systems must be ready to intervene at all times. Teslas using the system have crashed into semis crossing in front of them, stopped emergency vehicles and a roadway barrier.

A message was left early today seeking comment from Tesla, which has disbanded its media relations office.

In June NHTSA ordered all automakers to report any crashes involving fully autonomous vehicles or partially automated driver assist systems.

The measures show the agency has started to take a tougher stance on automated vehicle safety than in the past. It has been reluctant to issue any regulations of the new technology for fear of hampering adoption of the potentially life-saving systems.