A system and method for safely slowing or stopping a vehicle by selectively replacing a genuine engine control signal with a spoofed engine control signal to slow or stop a vehicle in a gradual or stepped manor. The operator is allowed control of the vehicle (e.g. genuine engine control signal) if the speed is below a threshold speed and the operator is denied control of the vehicle (e.g. spoofed engine control signal) if the speed is above the threshold speed, thus forcing the vehicle to slow to the threshold speed. The threshold is gradually reduced over time, causing the operator to stop the vehicle.