Making a vehicle stop for a police officer can be very dangerous for the officer and frightening for the person being stopped. Police officers generally follow the same general protocol.
A police officer cannot legally stop a car unless the driver has violated a law (typically criminal or vehicular in nature) or the officer has a "reasonable suspicion" that the driver is about to engage in criminal activity based on specific and articulable facts and inferences.
"Run" the Number Plate
Prior to stopping a vehicle, it is common practice to "run" the cars plates; that is, to input the car's number plate number into the state motor vehicle database to learn who the vehicle belongs to, and whether or not the owner or driver has any outstanding warrants or other violations.
After the driver's information is obtained, the law enforcement officer changes his status to Code 3, a response used to describe a mode of response for an emergency vehicle responding to a call.
Once the driver has stopped, the officer should park a minimum of 20 feet behind the vehicle and offset his/her alignment inside the driver's car.
Police officers ideally approach the vehicle quickly but cautiously, trying to be observant of how many people are in the vehicle, their movements and the driver's mannerisms.