When the framers of the constitution drafted the 4th amendment, it is safe to say they could not anticipate the invention of the automobile and certainly not their essential function in the daily life of Americans. Fortunately, the constitution was designed as a fluid instrument, as to prevent the government from denying essential protections to new technologies. As a result, we all have certain rights when it comes to traffic stops which prevent law enforcement from taking certain actions.
The Fourth Amendment prevents the government from performing unreasonable searches and seizures. A traffic stop would be considered a seizure under the Fourth Amendment and in order to be shown as reasonable, the officer needs to show that there is reasonable suspicion to pull over your car. In other words, he or she needs to show that there is a reasonable or articulable suspicion that there is criminal activity afoot. So if you have committed some kind of traffic violation in the officer’s presence, the Fourth Amendment won’t help you. But, if you have not committed any crime and the officer has no reason to think that you have committed a crime, he or she has no legal right to pull you over and thanks to the exclusionary rule, any evidence found against you as a result of that stop likely cannot be used at trial.
If the officer did have reasonable suspicion to pull you over, a subsequent investigation could still be unlawful. Let’s say for example you were pulled over by an officer for a broken tail light. In this case, you have committed a violation in the officer’s presence and there was reasonable suspicion to make you stop your vehicle so the violation can be addressed. He then writes you a ticket and hands the ticket over to you, thus addressing the violation. However, once the violation has been addressed, if the officer wants to perform a further investigation, he or she must show grounds which provide a reasonable and articulable suspicion which justifies further delay or show that you consented to a search. So if you were to refuse to consent to the search, the officer needs additional reasonable suspicion to continue the investigation. Additionally, a refusal to consent does not create reasonable suspicion, so there is nothing to lose by refusing to consent to a search. If the officer were to search you or your car with no consent and no reasonable suspicion, the evidence against you would again be likely inadmissible under the exclusionary rule.