Stopping a car with unintended acceleration isn’t as dramatic as the news media would have you believe. The above video explains the process in language any driver can understand. Here's what the video shows:
1) First, move the gear selector for Drive to Neutral. On a Prius, this is done by moving the selector to the left.
2) Putting the transmission ointo neutral should return the engine to idle. Apply your brakes and coast to a stop.
3) If the transmission won't go into neutral, step on the brake pedal as hard as you can. The brakes are stron enough to stop the car, even under full throttle acceleration.
4) When you've stopped the car, shift the transmission into park. Press and hold the start button until the motor shuts off.