Did the officer have reasonable suspicion of a DUI violation?

Last Modified: August 10, 2023

Did the officer have reasonable suspicion of a DUI violation?

A police officer needs reasonable suspicion of unlawful conduct to stop a motorist. The types of driving transgressions that result in an officer’s reasonable suspicion of a DUI violation vary greatly. There are several reasons for this variation: reasonable minds can disagree on the question of what is reasonable suspicion; the facts differ in every case; and states have different statutes making up what constitute traffic violations.

The first question to examine in determining the lawfulness of a motor vehicle stop is whether or not the police officer personally observed some violation of law.


Did the officer personally observe a traffic violation?

Although there are many incidents when an officer does not have to observe a violation of law in order to stop a motorist, the bulk of drunk driving stops are initiated because the officer claimed a traffic violation occurred in the officer’s presence.

The United States Supreme Court has found that it is not reasonable to stop a car for the sole purpose of performing a license and registration check. In that case, the officer said he stopped the car because, in his own words, “I saw the car in the area and wasn’t answering any complaints, so I decided to pull them off.” The Court decided that this was not reasonable and set forth the following standard to stop a car:

Accordingly, we hold that except in those situations in which there is at least articulable and reasonable suspicion that a motorist is unlicensed or that an automobile is not registered, or that either the vehicle or occupant is otherwise subject to seizure for violation of law, stopping an automobile and detaining the driver in order to check his driver’s license and the registration of the automobile are unreasonable under the Fourth Amendment. [Delaware v. Prouse, 440 U.S. 648, 663 (1979).]

The key phrase is whether or not the officer had an “articulable and reasonable suspicion” of unlawful activity. The officer need not have probable cause to stop a motorist. The probable cause standard is the standard used to determine the propriety of an arrest—not a detention.

The articulable and reasonable suspicion standard is an admittedly amorphous guidepost for evaluating the lawfulness of a motor vehicle stop. DUI lawyers and police have the same problem of trying to determine what is “reasonable suspicion” of unlawful conduct. The main difference between a police officer’s determination and a DUI lawyer’s is that the officer has less time in the field to make the appropriate assessment than the attorney has in the confines of his or her office.

While it is fair to recognize that an officer in the field must make a quick determination based on the facts at hand, a misapplication of those facts does not make a DUI stop lawful. In these cases, a good DUI lawyer will acknowledge to the court the sincere efforts by the police officer, but note that the law must still be followed. Good faith in a warrantless detention is not an exception to the requirement that the officer have objectively reasonable suspicion of unlawful conduct prior to making an enforcement stop.

Pretext stops

An improper motivation for the DUI stop (except for ones involving equal protection issues) does not invalidate the stop. If the police officer has an objectively reasonable basis for making a stop—i.e., a traffic violation—it does not matter that the real reason the defendant was pulled over was so the officer could look for drugs. The United States Supreme Court has approved pretext stops.

Common reasons for traffic stops

While there are almost an unlimited number of reasons an officer may use as a basis for conducting a motor vehicle stop, there are a few regularly recurring reasons for enforcement stops that result in DUI charges. The following are some examples of common reasons for traffic stops, and show how courts across the country come out differently as to which violations do or do not justify a DUI stop.

Weaving within the lane

Courts have found that weaving within the lane provides an officer with reasonable cause to stop a vehicle on suspicion of driving under the influence where such weaving continues for a substantial distance. In one California case, the substantial distance was ¾ of a mile. Courts have also found that “continued weaving” within the lane justified the stop.

Other courts have found that weaving within the lane did not permit detention of the vehicle or that touching the lane is not weaving out of the lane and is not a violation of the law. In one Texas case, an officer followed the driver for approximately a mile and a half. The officer estimated he saw the driver’s vehicle weave within the lane between two and seven times. The court found the detention unlawful particularly in light of the fact that the officer was not certain how many times the driver had weaved within the lane.

Weaving across the lanes

Some courts have held that weaving across the lanes numerous times permitted a DUI stop. In particular, one Kansas court found that driving across the centerline three times combined with speed changes and weaving inside the lane permitted the DUI stop.

Yet other courts have found that weaving across lanes does not justify the traffic stop. One Florida court held the stop was not proper when the defendant drove over the right hand edge line on three occasions, but did not travel significantly into the emergency lane; and there were no other vehicles in the vicinity. In another case in Maine, the court found that the defendant’s straddling of the centerline for approximately 25 to 50 yards did not justify the traffic stop especially given the sparse traffic on the highway.

Driving too slowly

Sometimes driving too slowly justifies a DUI stop while other times it does not. One Georgia court found a detention for driving too slowly was justified when the defendant was driving on the interstate at such a reduced speed that it constituted a safety hazard.

In another case, a DUI stop was justified because the driver did not respond quickly enough to a traffic light change. The driver remained stopped at a flashing red light for ten seconds. A police officer honked his horn at him, and he remained at the flashing red light for an additional 15 seconds. The Montana court held the ensuing stop was appropriate. However, in another case, a New Jersey court found a stop not appropriate based on the fact that the officer stopped the defendant simply because the defendant waited five seconds to proceed after the light at the intersection turned green.

In other cases, courts have found there was no reasonable suspicion to stop drivers who were traveling under the speed limit. In one such case, a Georgia court found there was no reasonable suspicion to stop the defendant who was traveling 25 to 30 miles per hour in a 55 mile an hour zone. Also, on highways that do not have designated minimum speed limits, courts have found that officers lack a valid basis to stop drivers for driving too slowly.

Car equipment violations

Some drivers are found to have been lawfully pulled over for equipment violations. For example, a detention in Texas was held proper due to the fact that the defendant was driving a vehicle that did not have a license plate light. In another case in Texas, the stop was held justifiable when a car’s license plate was improperly resting against a tissue box on the rear dash of the vehicle.

One California court held a detention was proper because the license plate was partially obscured, which violates a California vehicle code regulation that requires license plates be clearly visible. In another case, an officer stopped a car for illegal tinted windows. The windows were in fact illegally tinted, although the officer was mistaken in his understanding of the law as it pertained to tinted windows. Nonetheless, the Ninth Circuit found the stop justified because the officer had an objective basis to believe the window tinting constituted an equipment violation.

However, in other cases, courts have found that a good faith mistake of law did not render a stop lawful. In one such case, an officer’s good faith mistaken belief as to how many license plates the state of Michigan issued was the basis of the vehicle stop. The Ninth Circuit held that a good faith mistake of law did not render the stop lawful. The court distinguished its holding in this case from the above tinted window case by noting that the defendant’s windows in the tinted window case did have illegal tinting, and the officer was just unaware of the full nature of the law with respect to window tinting.

Squealing tires

Stops made after the driver was heard with squealing tires have been found justified in some cases and unjustified in others. In a Texas case, the officer was found to be justified in stopping a defendant whose tires broke traction spinning and screeching.

While in a Florida case, a stop was held not to be justified after an officer observed the defendant exit a hotel parking lot with tires squealing. No other unusual driving was observed by the officer.

Facts are paramount in DUI cases

As you can see from the above cases, courts across the country come out differently as to which violations do or do not justify a traffic stop. When a knowledgeable DUI lawyer has a case with one of the above common reasons for a traffic stop, he or she knows the law is important, but will use the facts in the case to make distinctions from cases that would seem to be controlling. Ultimately, it is the facts in every case that determine what is reasonable suspicion. It is the facts that will carry the day. Good DUI lawyers develop the facts in every case, and then find cases to support their position.

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