FAILURE OF VEHICLE TO ENGAGE AUTOMATIC EMERGENCY BRAKING OR APPLY ADAPTIVE CRUISE CONTROL BRAKING IN REPSONSE TO A VEHICLE ABRUPTLY STOPPING AHEAD. VEHICLE HAD ADAPTIVE CRUISE ENGAGED AT 57 MPH ON INTERSTATE HIGHWAY AND AN ACC SENSITIVITY OF 2. VEHICLE FORWARD COLLISION WARNING DID ALERT. THIS FAILURE RESULTED IN A REAR-END COLLISION WITH THE CAR AHEAD.