California’s DUI laws can be complex and confusing. In this section, our attorneys break down the rules and explain the process.
There are several tests that measure the amount of marijuana in someone’s system. However, they are unreliable for cases of driving under the influence of drugs (DUID), largely because there is no “legal limit” for marijuana. Without a test that is similar to a breathalyzer for drunk driving, police still have to use faulty drug impairment evaluations.
While there are some devices that claim to be able to measure marijuana in a breath sample, none of them has proven to be reliable enough for drugged driving cases. This is because there is little scientific evidence that reliably pin drug impairment to a specific test reading.
Drunk driving cases rely heavily on alcohol breathalyzers and other breath tests to determine whether a driver is impaired by alcohol. These portable breath tests measure the amount of alcohol in the driver’s breath. A suspect’s breath alcohol content (BrAC) is associated with his or her blood alcohol content (BAC). A BAC at or above 0.08 percent is considered legally intoxicated.
Drugged driving cases, though, need drug tests that detect a variety of controlled substances. For marijuana DUI cases, law enforcement agencies have claimed that the substance is tetrahydrocannabinol, or THC. This substance is the most prevalent compound in marijuana and is the drug’s psychoactive ingredient.
Some devices have been made that can detect THC in a breath sample. Some of those devices claim to detect very small amounts of THC in a person’s system – down to several parts per trillion.1
However, there is very little evidence that a specific level of THC makes someone too impaired to drive a car.2 While THC is known to affect memory, judgment, and fine motor skills, studies found that the levels of THC in breath, saliva, or other fluids did not reflect the level of impairment that a person was experiencing.3
As a result, the accuracy of these THC tests is meaningless.
Nevertheless, some states have laws that allow THC levels to be presented as evidence of impairment. Some of these laws were passed in response to the legalization of marijuana for recreational use. In Colorado, for example, it is a permissible inference that the driver was impaired by marijuana if he or she had more than 5 nanograms of delta-9-THC per milliliter of blood.4 Overcoming this inference can take the skills of a criminal defense attorney or DUI lawyer.
Without a reliable test to determine marijuana impairment, police often use a drug recognition expert, or DRE. These are police officers who have special training in identifying marijuana use or whether someone is under the influence of another form of narcotic.
Not all jurisdictions have the same rules for DREs. Some states or counties do not have DREs, at all. Where they are not available, the officer who initiated the traffic stop will perform the DUI investigation.
In California, if an officer initiates a traffic stop and suspects drunk driving, but the driver does not show signs of alcohol impairment, he or she will call a DRE. Once on the scene, the DRE will take over the DUID investigation. The DRE will conduct the following 12-step evaluation:
Generally, drivers can refuse non-chemical BAC tests without violating their state’s implied consent law.
Evidence gathered by DREs is frequently challenged in court. By establishing an attorney-client relationship with a DUI attorney or DUI-defense lawyer, drivers can fight their DUI charges.
No. Unlike for drunk driving, there is no per se legal limit for drugged driving.
A legal limit is the amount of alcohol or drugs that is presumed to make someone unable to safely drive a motor vehicle. For drunk driving, that limit is a BAC of 0.08 percent. There is only 1 state where it is different: In Utah, it is 0.05 percent.6 States also use different legal limits for:
For drugged driving, there is no established legal limit. Some states have passed laws that set “soft legal limits” on drivers under the influence of marijuana. Colorado is an example. There, evidence that a driver had at least 5 nanograms per milliliter of blood creates a permissible inference of intoxication.7 However, there are no states that have a per se limit like those used for drunk driving.
For more discussion, see our page on Do breathalyzers detect weed?
A former Los Angeles prosecutor, attorney Neil Shouse graduated with honors from UC Berkeley and Harvard Law School (and completed additional graduate studies at MIT). He has been featured on CNN, Good Morning America, Dr Phil, Court TV, The Today Show and Court TV. Mr Shouse has been recognized by the National Trial Lawyers as one of the Top 100 Criminal and Top 100 Civil Attorneys.
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