When an officer pulls over a driver, it's considered a "detention"—the driver hasn't been arrested, but nevertheless isn't free to leave. This article explains when an officer can legally stop a motorist and some of the nuances of the laws that apply to traffic stops.
Where a typical traffic detention is concerned, officers generally must have reasonable suspicion that the driver or someone in the vehicle is committing or has committed a crime. (Though exceptions, such as sobriety checkpoints, do exist.)
In other words, police generally can't just make a traffic stop because they have a hunch something is amiss. For a traffic stop to be legal, police normally need an objective reason to believe someone has broken the law, though a minor traffic violation is usually enough.
In Delaware v. Prouse, the Supreme Court considered the case of a man prosecuted for marijuana possession. (440 U.S. 648 (1979).) In the course of a traffic stop, the police officer had seen marijuana on the defendant's car floor.
The officer testified that he hadn't seen the defendant's vehicle violate any traffic laws before he conducted the detention. He hadn't observed any equipment violations, nor had he witnessed any suspicious activity. He enforced the stop only so that he could check the driver's license and the vehicle's registration. He wasn't acting in accordance with any established guidelines or procedures. The Court held that his kind of "spot check," left entirely to the police officer's discretion, is unconstitutional.
Every situation is a little different. In some scenarios, it might be obvious that the police had a reason to pull you over. For instance, if you ran a stop sign or were speeding, you've broken a law and the police are certainly justified in making a traffic stop.
However, in other cases, the reason for a traffic stop might not be so clear and the legalities might be debatable. But, whatever you might think about why an officer pulled you over, there isn't much you can do about it at that moment. Arguing with an officer is typically a bad idea. Anytime you get pulled over, being courteous and compliant with law enforcement is the way to go.
The time and place to dispute the legality of a traffic stop are in court. If you believe you were unlawfully detained by police, get in contact with an attorney who can help you. A qualified attorney can review the police report, assess your case, and let you know if you have any viable argument that the traffic stop was illegal. If a judge agrees that the stop was unlawful, you might be able to get the case thrown out with a motion to suppress evidence or through some other legal avenue.
In terms of a DUI arrest, the original stop might or might not be based on an officer's suspicion of drunk driving. For instance, officers normally pull drivers over when they observe indications of impairment such as swerving or ridiculously slow driving. But in other cases, an officer might stop a motorist for a minor traffic violation (like a stop sign or speeding violation) and notice signs of intoxication (like the odor of alcohol) during the traffic stop. In both situations, the stop is valid, and the officer is allowed to conduct a reasonable DUI investigation.
The legality of the traffic stop is just the first part of the analysis. For a DUI prosecution to be lawful, the driver's arrest must be supported by probable cause. In other words, police need a reasonable basis to believe the motorist was driving under the influence.
In most states, a DUI is defined as being in actual physical control of a vehicle while:
In some cases, the motorist's driving pattern will provide some of an officer's probable cause. And during the stop, the officer might note other symptoms of drug or alcohol use such as:
It's also common for officers to ask drivers to complete field sobriety tests (FSTs) or a roadside breath test. FSTs and prearrest breath tests are typically optional. But if a driver consents, the results are fairly considered in the probable cause determination.
If, on balance, the facts could lead a reasonable person to believe the driver is under the influence, the officer is legally justified in making a DUI arrest.
So, what happens if there was no reasonable suspicion for the stop or probable cause for the arrest? Generally, any evidence obtained subsequent to the illegal police action will be inadmissible in court.
To exclude illegally obtained evidence from consideration at trial, a defendant would normally need to file a motion to suppress evidence in court. A successful motion to suppress can ultimately lead to the dismissal of a DUI charge. (Of course, a motion to suppress is just one of the many ways to fight a DUI charge.)
If you've been arrested or have questions about the legalities of a traffic stop, get in contact with a qualified attorney. An experienced attorney can tell you how the law applies to the facts of your case and help you decide on the best course of action.