Bi-directional PID control
Chris is correct and PID commonly operate to give positive and negative outputs - even your car cruise control example is out of data, modern radar controlled cruise controls can indeed operate the brakes as well as the throttle.  A more general example is called a servo.  Small scale ones are used for models.

Here is another example of an Arduino using a PID loop to balance a beam in a different way:

Beam balancing example