While cannabis consumption is legal in California, driving under the influence of any intoxicating substance remains prohibited. Highway patrol officials have the authority to stop an individual who appears intoxicated while operating a motor vehicle. Obtaining accurate impairment levels from cannabis consumption, however, is a challenge because reliable roadside test results are difficult to produce, according to NBC News.

Swerving in and out of lanes, slurred speech or appearing generally unfocused may result in a field sobriety test to gauge a driver’s cognizance. To determine whether a driver’s alcohol consumption is within the legal limit, law enforcement may administer a roadside breath test. Breath test results are available quickly, so an officer can make an arrest when drivers show a BAC higher than 0.08%. This is not the case, however, with cannabis field testing.

Cannabis intoxication levels vary with each individual

The amount of cannabis necessary to produce an intoxicating effect varies with each driver. There is no current and established standard for measuring an individual’s impairment level from its intoxicating ingredient, tetrahydrocannabinol. Studies also show that there is no definitive correlation between an individual’s THC consumption and the degree of intoxication.

Because THC is fat soluble, it may stay in a person’s bloodstream for many months after its ingestion. Until the compounds break down and become metabolized by the body, THC may appear in an individual’s blood or urine even when he or she was not impaired. A road stop blood or urine test may not produce a result which is reliable enough to determine the intoxication level from cannabis consumption.

Law enforcement may test for cannabis intoxication at a road stop

Since highway patrol officials may not have access to a reliable roadside laboratory, a standard cognizance test determines cannabis impairment. Some California law enforcement officials use advanced techniques for testing a driver’s cognizance. As reported by the Los Angeles Times, authorities will typically use a 12-step examination and an individual’s pulse or blood pressure reading to determine if there is impairment.