Adaptive-cruise-control (acc)/forward collision braking(avoidance) system applied very strong brakes(twice) in certain scenario when using acc, increasing the chances of vehicle behind rear-ending. while acc is enabled, say your vehicle comes to fullstop as vehicle in front has come to a full stop(say at traffic signal) and acc applies full brakes. traffic ahead starts moving again, but since vehicle won't move on its own driver is required to press accelerator to get it moving again or acc to resume its operation (this is by design). in such scenario if driver ends up pushing accelerator a bit harder(i.e. more than just tapping it), acc applies very strong brakes stopping vehicle right there. by this time vehicle behind you has started moving already and might rear-end due to abrupt stop. i guess acc thinks distance between you and vehicle ahead is very less and thinks its going to collide and hence applies strong brakes. but this is a bad design/programming since it expects driver to push acc. pedal for acc to resume operations, but if driver does it bit more than what acc likes, there is a chance of accident. gm should perform more tests with its acc around such scenarios and fine-tune their acc software. *tr