Drunk driving charges all start somewhere, and it's usually the time the police officer pulls you over. There's the conversation, maybe some questions about your alcohol consumption, and a few roadside tests before a possible arrest and DUI charge.
But let's back up -- cops can't pull you over for no reason, right? And if officers had no reasonable suspicion to stop you, that could mean that everything that happens after you're pulled over is inadmissible in court. So here's a look at DUI traffic stops, and how they affect your case.
There is a long-held legal doctrine under search and seizure law known as the exclusionary rule. Under this rule, any evidence that was illegally obtained by police can't be used against a suspect in a criminal prosecution. The exclusionary rule also applies to legally obtained evidence only gathered after an illegal action. Known as "fruit of the poisonous tree," this evidence is also inadmissible.
In the DUI context, if the initial traffic stop is improper (the tree, in this metaphor) even if there is properly obtained evidence of drunk driving, like a breathalyzer sample, that evidence (the fruit) could not be used against you at trial and may lead to your DUI charges being dismissed.
As an initial matter, police need reasonable suspicion of criminal activity in order to pull you over or stop your car. (Note: this does not apply to DUI checkpoints, at which officers may randomly stop vehicles under certain limitations.) Reasonable suspicion for a DUI stop is normally based on bad driving: drifting between traffic lanes, illegal turns, erratic speed changes, or stopping for no particular reason. Any traffic violation can be a valid reason for police to stop your vehicle, and, once you are stopped, initiate a drunk driving investigation.
If an officer pulls you over without reasonable suspicion, any evidence of drunk driving obtained after that could be inadmissible. So even if you failed some roadside sobriety tests or had high reading on a breathalyzer, if the stop itself was illegal your DUI arrest would be illegal as well.
It is important to note, however, that challenges to the legality of your traffic stop will come later, and refusing to cooperate with an officer just because you don't think he should've pulled you over typically is not in your best interests. If you've been charged with a DUI and you think officers illegally stopped your car, contact an experienced DUI attorney to review your case.