A driver can be arrested for driving under the influence even if the driver tests under the legal threshold of 0.08% blood alcohol content (BAC) or even a 0.00% BAC.  If the arresting officer has probable causeto believe that the driver’s ability to drive is impairedby any substance— be it alcohol, legal or medically prescribed cannabis, or any prescription drug (whether legally prescribed or not)—there are grounds for the arrest . When a driver tests over the per se limit of 0.08% BAC,  probable cause is presumed, but how does the officer determine that the driver’s ability to drive was impaired  when there is no obvious  symptom or immediate chemical test to establish probable cause?

It may boil down to the subjective evaluation of the officer.  In such cases, the prosecution will have the burden to prove the probable cause. Because this is often a subjective evaluation, an experienced DUI defense attorney may be able to get the charge dismissed.

What is impaired driving? Under California law, a driver is impaired when alcohol or a drug affects the driver’s brain, muscles, or nervous system to the degree that the driver’s “ability to operate a vehicle in a manner like that of an ordinarily prudent and cautious person in full possession of his faculties” is compromised.  (People v. Enriquez (1996) 42 Cal.App.4th 661, 665.) Driving under the influence implicates a greater impairment than simply being under the influence. In other words, a person could be on a prescription medication that somewhat affects the nervous system (for example) or have a slight buzz after one drink (and still under 0.08% BAC) but still be able to drive as safely as a completely sober driver. This may be up for dispute given some recent studies that suggests even small amounts of alcohol or marijuanaaffect a driver’s reaction times and other safe driving conduct, but it still remains the prosecution’s burden to prove the driver was impaired.

The definition provided by the Enriquezcase still doesn’t satisfy; it is still a subjective determination. So what facts may the prosecution rely on to prove the driver was not as safe on the road as an “ordinarily prudent and cautious” driver? Obvious evidence might include testimony or statements by witnesses or police officers that the driver was driving in an erratic manner, for example, weaving or driving at inconsistent speeds. But what if the driver exhibited no such driving evidence but was stopped by an officer for, say a busted tail light, and upon contact, the officer thought the driver appeared high?

The California Supreme Court has distinguished “being under the influence” from “driving under the influence. “ In the former, one may be guilty if he or she is “in that state in any detectable manner.” (People v. Canty (2004) 32 Cal.4th 1266.)  Unlike driving under the influence, there is no requirement that a person “demonstrate impairment of physical or mental ability.” (Id.)

Taking our hypothetical driver with the busted tail light, let’s say the officer observed that his eyes were red and the officer detected a slight smell of marijuana on his clothing. Based on these observations, the driver was arrested for driving under the influence of marijuana and even tested positive for THC (although, as I have discussed elsewhere on this blog, that test tells law enforcement little about the driver’s state at the time he was driving). If the prosecution cannot establish that the driver was impaired by his alleged marijuana consumption, the charge of driving under the influence has a good chance of being dismissed.

When a DUI arrest is based only on an alleged impairment of the driver’s ability to drive safely, there must be some evidence that supports that. Even if it is established that the driver did have a drug or alcohol (less than 0.08% BAC) in his or her system, without some evidence of actual impaired driving, the charge is susceptible and with a proper defense can be defeated.

Whether there was evidence of impaired driving or not, there are a number of defenses to a DUI charge that may end in dismissal of the charge or to a reduced charge or sentence.  Orange County DUI defense attorney William Weinberg can help. Contacthim for a free consultation regarding you option at (949) 474-8008 or by email at

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