Under the Fourth Amendment, police officers must have a certain level of justification before they can lawfully make a traffic stop or arrest you. In the context of drunk driving, the law requires that officers demonstrate reasonable suspicion for a traffic stop and probable cause for an arrest.
These standards apply in all types of DUI cases, including:
- Vehicle Code 23152(a) – driving under the influence,
- Vehicle Code 23152(b) – driving with a BAC of 0.08% or greater,
- Vehicle Code 23140 – underage driving with a BAC of .05% or greater,
- Vehicle Code 23152(f) – DUI of drugs (“DUID”),
- Vehicle Code 23152(e) – commercial driver DUI.
As a result, a defense strategy often includes a challenge to reasonable suspicion/probable cause. This is usually done by filing a Penal Code 1538.5 PC motion to suppress evidence. 1 2 3
To help you better understand the probable cause or reasonable suspicion needed for a traffic stop, investigation and arrest, our California DUI lawyers discuss, below:
- 1. What is probable cause for a DUI stop?
- 2. When can police start a DUI investigation?
- 3. What do police need to make a DUI arrest?
- 4. What if I am arrested without probable cause?
- Additional Resources
1. What is probable cause for a DUI stop?
To pull you over for driving under the influence, the police or California Highway Patrol (CHP) officer must have “reasonable suspicion” that a crime is or was taking place. This is similar to, but not exactly the same thing as, “probable cause.”4
The Fourth Amendment to the United States Constitution prohibits unreasonable searches and seizures.5 This means an officer cannot pull you over for no reason. Instead, they must be able to point to specific facts that led them to suspect that a crime was taking place.6
The 4th Amendment to the US Constitution is the origin of the “probable cause” requirement in California law.
This does not mean the officer must specifically suspect you of DUI. Any potential traffic infraction or violation is enough “reasonable suspicion” for a stop.
Example: Jeannette, a police officer, observes a car driving away from a street where a number of bars are located. She then sees the driver run a stop sign. She also notices the driver has tinted windows in violation of Vehicle Code 26708.
Specific facts that could support a reasonable suspicion that the driver is under the influence include:
- The vehicle coming from an area with a large number of bars, and
- The driver running a stop sign (Vehicle Code 22450).
There is one exception to this “reasonable suspicion” rule: The police do NOT require reasonable suspicion of a crime to stop you at a lawful sobriety checkpoint.7
2. When can police start a DUI investigation?
Law enforcement officers need reasonable suspicion to begin a “DUI investigation.” The investigation is the next step after a traffic stop or sobriety checkpoint.
An investigation begins when an officer believes you may be guilty of driving under the influence. This investigation usually involves:
- Questions about whether, where, and how much you had been drinking;
- One or more field sobriety tests (FSTs); and/or
- A preliminary alcohol screening (PAS) test with a handheld breathalyzer.
In some counties, an officer may also swab your cheek if the officer suspects DUI of marijuana.
Note that you are not required to take any of these tests BEFORE an arrest.
Note, too, that as each phase of a DUI stop progresses, there is a slightly higher requirement for the level of justification needed. It may be fairly easy for an officer to satisfy the reasonable suspicion required for a traffic stop. However, the level of cause needed to detain and investigate you is higher.
A field sobriety test is typically part of a drunk driving investigation.
More Than a “Mere Suspicion” Is Required
For an officer to legally detain and investigate you for driving under the influence, they must be able to identify certain specific facts. These can be any facts that would lead a reasonable officer to suspect that you are breaking California laws.
For example, if you are stopped at night, officers will likely ask you if you have been drinking. Even if you consumed only a marginal amount of alcohol, a yes answer may be enough to create the cause needed for an investigation.
Other facts that might create enough cause for an officer to detain and investigate you include:
- The officer observes an open container of alcohol in your car;
- The officer smells alcohol on your breath; and/or
- The officer observes red/watery eyes, a flushed face and/or other physical symptoms consistent with driving under the influence.
3. What do police need to make a DUI arrest?
An officer must have probable cause to make an arrest for driving under the influence.8 The officer must be able to point to specific facts that show why they believe you are under the influence. A mere hunch or vague suspicion will not suffice.
Facts that might constitute probable cause include:
- A high blood alcohol content (“BAC”) result on a preliminary breath test,
- Poor performance on field sobriety tests, or
- Distinct physical signs of intoxication (such as slurred speech or dilated pupils).
Probable cause is required for an arrest in California.
The officer will not necessarily share these facts with you at the time of the arrest. Though they should be in the police report.
More importantly, the officer must be able to convince the court that the “probable cause” standard was satisfied.
4. What if I am arrested without probable cause?
The most common remedy for an unlawful DUI stop, investigation, or arrest is a PC 1538.5 motion to suppress evidence.9
A motion to suppress is based on a legal principle known as the “fruit of the poisonous tree”. It means that if any stage was improper (the “tree”), anything that the officer discovers as a result (the “fruit”) is tainted.
Therefore, this “fruit” is subject to “suppression.” When a judge “suppresses” evidence, it means that such evidence may not be used against you.
Example: A San Diego Police officer pulls over a black man driving an expensive car even though he committed no traffic violation. The officer asks the driver, George, if he was drinking or using. George said he smoked one joint.
The officer asks George for a marijuana swab (which is being tested in some California counties). When it comes up positive, he arrests George and requires a blood test to test for drugs. The blood test comes up positive for marijuana.
George’s defense lawyer will probably file a motion to suppress the blood test results. The lawyer will argue that because George obeyed all the traffic laws and showed no signs of intoxication, there was insufficient cause for the officer to arrest him.
It is important to note that PC 1538.5 motions to suppress for lack of probable cause usually are not granted in DUI cases. However, as Oakland defense attorney John Murray10 explains:
“Many experienced California criminal defense lawyers will still run a motion to suppress for lack of probable cause for strategic reasons. This is an important pre-trial opportunity to cross-examine the officer and to discover any weaknesses in the prosecution’s case–weaknesses that may result in reduced or even dismissed DUI charges down the line.”
Additional Resources
For more information, refer to the following:
- Alcoholics Anonymous – 12-step program for overcoming alcoholism.
- Drunk Driving Overview – NHTSA page on drunk driving statistics and prevention.
- Impaired Driving: Get the Facts – CDC fact sheet on impaired driving.
- Driving Under the Influence (DUI) – California DMV page on driver license suspension for DUIs.
- MADD – Non-profit organization devoted to stopping drunk driving.
Legal references:
- Terry v. Ohio, (1968) 392 U.S. 1, 20.
- United States Constitution, amendment IV.
- Penal Code 1538.5 PC – Motion to return property or suppress evidence. (“(a)(1) A defendant may move for the return of property or to suppress as evidence any tangible or intangible thing obtained as a result of a search or seizure on either of the following grounds: (A) The search or seizure without a warrant was unreasonable [as may be the case with California DUI arrests made without probable cause].”)
- Terry v. Ohio, endnote 1 above.
- United States Constitution, amendment IV.
- Terry v. Ohio, endnote 1 above, at 21 (“And in justifying the particular intrusion the police officer must be able to point to specific and articulable facts which, taken together with rational inferences from those facts, reasonably warrant that intrusion [with respect to a California DUI investigation].”)
- Ingersoll v. Palmer (1987) 43 Cal.3d 1321, 1327. (“[T]he primary purpose of the [DUI checkpoint] stop here was not to discover evidence of crime or to make arrests of drunk drivers but to promote public safety by deterring intoxicated persons from driving on the public streets and highways. We therefore conclude the propriety of the sobriety checkpoint stops involved here is to be determined not by the standard pertinent to traditional criminal investigative stops [reasonable suspicion/probable cause], but rather by the standard applicable to investigative detentions and inspections conducted as part of a regulatory scheme in furtherance of an administrative purpose.”)
- United States Constitution, Amendment IV.
- Penal Code 1538.5 PC — Motion to return property or suppress evidence, endnote 3 above.
- Oakland DUI defense attorney John Murray is a leading expert in California DUI defenses, including lack of probable cause or reasonable suspicion for DUI traffic stops, investigations and arrests. He has extensive experience both in the court systems of Los Angeles County and Ventura County and in California DMV hearings.