Marijuana and DUI: How Will Civil Courts Determine Liability?

How Do We Know Exactly When A Driver Is Impaired?

We had a big march to legalize marijuana here in Fort Worth last weekend. Lots of people smoke it — and any personal injury lawyer in Texas has seen his share of crashes caused by those driving under its influence.

But at what point is someone so high that they are too impaired to be driving? If a blood test is taken later, can its findings be admitted? Can they be automatically found to be negligent in a civil trial for damages?

Police who suspect a driver has had too much to drink perform a Breathalyzer or blood test to measure the amount of alcohol in his or her system. Several studies have set .08 percent blood alcohol concentration (BAC) as the legal limit when a person is too impaired to drive and Texas uses this standard. OK, easy enough.

But marijuana also interferes with a person’s judgment, perception, vision and reaction time and  Texas law does not define a comparable legal limit for how much marijuana results in impairment.

Anything that distracts the driver, lowers response time or interferes with judgment and cognition is dangerous. This includes legal amounts of alcohol, marijuana and prescription drugs.

This doesn’t mean a person is permitted to drive under the influence of marijuana, just that the amount considered “safe” is vague. Of course, unless a driver has a legal prescription for marijuana, possession remains illegal in Texas, so any use is unlawful regardless of whether a person also drives.

AAA Foundation for Traffic Safety Study Reaches Surprising Conclusion

Although some people become drunk from less alcohol, the law generally recognizes that .08 BAC is the point at which a driver becomes unsafe. An AAA Foundation for Traffic Safety study could not definitively pinpoint such a limit in THC, the substance in marijuana that causes impairment.

Researchers tested impairment of people with a THC level of 5 nanograms per milliliter of blood, which is the impairment level established by Colorado, Montana and Washington. They found that some people were greatly affected at this level, while others exhibited no signs of impairment.

In addition, the long half-life of the drug depends on several factors, including frequency of use, potency and method of ingestion. Therefore, a frequent user might show high levels of THC in her or his system long after use, whereas an occasional user’s level would rapidly drop. This creates a legal challenge because justice could not be equally applied by setting a blood concentration level.

The AAA and Mothers Against Drunk Driving (MADD) recommend reliance upon observational, behavioral and psychological evidence, such as the results of field sobriety tests. For example, the smell of cannabis, combined with the driver’s bloodshot eyes, lethargy and swaying during the one-legged stand test would indicate impairment.

Alcohol Remains Number One Killer on Texas Roads

Alcohol remains the primary cause of fatal crashes in Texas. In fact, Texas still leads the country in numbers of drunk driving deaths. 1,446 people died in drunk driving accidents in Texas in 2015, equal to 40.9 percent of all traffic fatalities in the state that year and an increase of 8.2 percent from the previous year. Another 15,687 people were injured in alcohol-related accidents last year.

We know alcohol is horrifically dangerous and there are piles of studies to prove it. But studies about marijuana impairment are lacking.

How will this affect civil liability in car wreck trials? No one knows.


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