NHTSA Complaint #11535441 — 2022 BMW X5

East bound on US 20 and Barrington Road in Hanover Park IL. I was in the right lane and had stopped at the light, about 3rd or 4th car back. There was a semi-truck in the middle lane (on my left). Assisted Driving/Adaptive Cruise Control (Cruise Mode 2) was active. The car automatically accelerated from the light. When I entered the intersection, the car sounded a warning alarm and braked very hard momentarily, but did not stop the car. I was quite startled and did not notice an alert in the dash. Braking was so hard and so sudden I felt lucky that I was not rear ended by the car behind me. There was nothing in my path. Just beyond the intersection there is a rail road overpass. The road curves slightly to the right just beyond the intersection and is slightly downhill to go under the overpass. There was a freight train on the overpass, all tanker cars I believe. My speculation is the car's sensors "saw" the freight train as a potential collision, perhaps cross traffic. and the car's safety systems were applied.