Adaptive cruise control was on, i was driving on the highway, traffic was speeding up and slowing down, and the tesla was braking accordingly. I was paying attention to the road and noticed, all of a sudden, that the tesla was not braking as traffic in front of us slowed. I immediately slammed my foot on the brake as hard as i could, yet there wasn't enough time or distance, and my car collided with the one in front of me. I wasn't injured, but there's a chance someone in the other car was. The emergency brake did not kick in whatsoever, and the adaptive cruise control completely failed, leading to an accident.