Cadillac 2011 STS Owner's Manual page 212

Adaptive Cruise Control may lose track of the
vehicle ahead and accelerate up to your set
speed while entering or on highway exit ramps.
You could be startled by this acceleration and
even lose control of the vehicle. Disengage
Adaptive Cruise Control before entering a
highway exit ramp. Do not use Adaptive Cruise
Control while entering or on exit ramps.
If another vehicle enters the same lane as you,
Adaptive Cruise Control will not detect the vehicle until
it is completely in the lane. Be ready to take action and
apply the brakes yourself.
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How well Adaptive Cruise Control works on hills
and while a trailer is being towed depends on your
vehicle speed, vehicle load, traffic conditions, and the
steepness of the hills. It might not detect a vehicle in
your lane while driving on hills. While going up steep
hills, you might want to use the accelerator pedal to
maintain your vehicle speed. While going downhill and
towing a trailer, you might might have to brake to keep
the vehicle speed down. When the brakes are applied
the cruise control is disengaged. You may choose not to
use Adaptive Cruise Control on steep hills when towing
a trailer.
Apply the brake pedal or move the Adaptive Cruise
Control switch to off, to disengage the system. Adaptive
Cruise Control information does not appear on the HUD
while the system is not engaged.