Simply Put, it's a Radar Gun that tells you the speed of the Vehicle that you gun it at. Yes, in order for this o be accurate, it would have to be a Raycast Weapon. It gets the Velocity of any Vehicle and displays it on the user's Screen.
Also, perhaps an RTB Pref, that checks the speed limit of the Vehicle, and if they are Gunned, it Uses a Modded Respawn Point and Spawns the Lawbreaking Vehicle, where the player would have to Buy it out using VCE Variables etc.
