The study is a reminder not only that the fully self-driving future many people imagine is a long way off, but also that a present in which cars can perform on their own some functions traditionally reserved for humans can prove dangerous. The NHTSA also recently upgraded a probe of Tesla Autopilot to an engineering analysis; investigators are examining the feature’s responsibility for repeated collisions with parked emergency vehicles such as ambulances and police cruisers — which drivers should have been able to see about eight seconds before impact, but which they