RAdio Detection And Ranging. If you wanted to you use RADAR, you would direct a short radio pulse in a certain direction. Large objects like ships and planes reflect some of the radio pulse back to you: Detection. If you then measure how long it takes for the reflected radio wave to come back, you know how far the object is from you: Ranging.

I suppose you're not looking for "Removing Aggressive Drivers and RoadRage", but an acronym finder might help you out!