They said the Tesla began to slow a second before the collision. They don't say if it was the driver or the AP/TACC/AEB nor by how much it slowed.AEB does not stop the vehicle. It merely reduces speed.
Like TACC does other than edge cases, such as a pickup truck making an illegal lane change just feet in front of a car.
What are we hoping for here? The Tesla driver is comfortable enough in the system to not pay attention, or perhaps he was paying attention but just entirely deferring driving authority to the AP.
He, no doubt, was assuming that his Tesla would not crash into things. He was wrong, but why was he wrong? One possibility is TACC did not sense the problem. Only the logs can answer that. Further, AEB did not sense the problem or respond adequately. It is designed to see this problem, the vehicle ahead is hardly stopped or slow-moving, AEB should really have done better.
Another possibility is the driver was pressing the accelerator thus preventing TACC or AEB from braking.
It will be interesting to find out what combination of conditions caused the collision. These cars are not supposed to just run into other moving cars. Something about the car, the sensors, the setup, or the driver's behavior caused it. Or a combination.
Without the collision there was no rollover and no need for the seatbelt. What caused the collision? The Tesla car/driver had time to avoid it