The US is investigating a 12th Tesla Autopilot crash involving an emergency vehicle

• The US highway safety agency has expanded its investigation into certain Tesla Autopilot crashes.
• The probe is looking into 12 incidents where Teslas collided with stopped emergency vehicles.
• NHTSA on Tuesday began asking Tesla about Autopilot and how it works.

The US government's highway safety agency expanded an investigation into Tesla Autopilot crashes to include a 12th recent incident.

The National Highway Traffic Safety Administration in August began investigating incidents where Teslas using the company's driver-assistance technology collided with stopped emergency vehicles. When it announced the investigation, it had identified 11 such incidents since 2018.

In a Tuesday letter to Tesla, the agency identified another crash it's looking into. The August 28 incident saw a Model 3 barrel into a Florida Highway Patrol vehicle and another stopped car outside of Orlando, Florida, local media reported.

Tesla did not return a request for comment.

When switched on, Autopilot keeps a Tesla centered in its lane and watches the car ahead to keep a steady distance. But it does not make cars drive themselves and requires full driver attention. One of its main limitations appears to be recognizing and slowing down for stopped vehicles.

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According to NHTSA, the initial 11 crashes under investigation led to 17 injuries and one death.

In Tuesday's letter, the agency asked Tesla to describe in depth how Autopilot functions, including how it recognizes elements of first-responder scenes like cones, flashing lights, road flares, and reflective vests. NHTSA also asked how dark conditions affect Autopilot's operation.

Tesla and other automakers have been developing advanced driver-assistance systems for years, but it's largely been the Wild West in terms of oversight. NHTSA has stepped up efforts to understand and improve these technologies as of late. In June, the agency began requiring automakers to report crashes involving their automated-driving systems.