Answer (Show when driving)

When it is safe, and you won't be distracted, turn on rear screen heater. There is normally a button near the fan and temperature controls, but will depend on the make and model of the vehicle. If the screen does steam up whilst driving you can also turn on Air Conditioning (AC), as this will help to remove the moisture from the air inside the car. It's useful to note that on most modern vehicles the rear screen heater control will also heat the door mirrors to improve visability.