Rules of the Road

If the legal limit for a DUI is .08, how can someone get a DUI if they blow less?

Woman tells her story of DUI arrest to prevent others from drinking and driving

Rochelle Fischer is shares her story about the night she got busted for a DUI in Bellingham, hoping others will learn from her mistake.
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Rochelle Fischer is shares her story about the night she got busted for a DUI in Bellingham, hoping others will learn from her mistake.

Question: If the legal limit for getting a DUI is .08, how can someone get a DUI if they blow less than .08? Wouldn’t they not be legally drunk?

Answer: Sometimes the words we choose to describe things change our understanding of them.

The term “legal limit” is a potentially disastrous example. You might infer from this term that there is a limit under which it is legal to drive after drinking. The law has no such limit.

Although “legal limit” often gets tossed around in conversations about impaired driving, people in the business of investigating or prosecuting DUI would more likely use “per se limit” or “presumptive limit.” These terms more accurately describe what .08 means to the law. (Side note: .08 refers to the amount of alcohol in a person’s blood, measured in grams per 100 milliliters.)

The presumptive limit, put simply, is the point at which the law has agreed everyone is impaired.

If you were to take a look at the RCW on impaired driving, you’d see a four-item list of what it takes to be found guilty of driving while impaired.

The first two items on the list are strictly measurements of substances in the blood; the first is alcohol and the second is THC. Essentially, if a person’s blood alcohol content (BAC) is above a .08, the prosecution doesn’t need any other evidence to prove guilt.

The next two items on the list address drivers who are “under the influence of or affected by” alcohol or drugs.

Alcohol begins to affect people at levels far below .08 blood levels. At around .03 our concentration gets worse. At around .06 our reasoning, depth perception, peripheral vision and glare recovery don’t work like they’re supposed to work.

All of the things I just listed are pretty important when driving. If a person is under the influence of alcohol and an officer observes that influence while the person is driving, that driver could be arrested for DUI, even with a BAC of less than .08.

The other word that isn’t really helpful when talking about DUI is “drunk.” Although we often talk about drunk driving, the law isn’t concerned with drunkenness but with impairment.

We all know what a drunk person looks like; slurred speech, staggering around, drunk-dialing your ex. Impairment can be more subtle. The affects of alcohol I listed above all happen before someone starts slurring their speech or loses their gross motor control.

There’s another way that someone might be impaired at levels far below the presumptive limit: poly-drug use.

Poly-drug use is the combining of two or more drugs. The most common occurrence is when people combine alcohol and marijuana, sometimes called crossfading.

When combining drugs, the effect is often greater than the sum of the parts. A person could have a BAC well below the presumptive limit, along with a THC content of less than five nanograms per milliliter of blood (the presumptive limit for THC) and still be impaired.

There are some other significant risks to crossfading, but I’ll keep this conversation limited to impacts on driving.

Deaths in Washington from impaired driving have increased in the last few years, and that can be attributed to poly-drug use, especially the combination of alcohol and marijuana.

The number of fatalities from people impaired only by alcohol has been decreasing, but deaths caused by drivers with two or more drugs in their system have shot up. Most frequently those two drugs are alcohol and THC.

While we’re on the topic of combining drugs, let’s not forget that we sometimes consume products that we don’t think of as drugs, even though they sort of are. I’m talking about things like coffee, tea, soda, Red Bull. These contain caffeine, technically a drug.

On its own, caffeine has become the drug of choice to help many humans survive yet another dreary morning meeting. But combining caffeine with marijuana can give different results than marijuana alone.

Mixing cannabis and coffee has come to be known as a Colorado speedball, clearly an indicator that people have figured out the impacts mixing them.

Even though we have a presumptive limit, impaired driving isn’t limited to a number. Lots of factors are involved in what kind of impact alcohol and other drugs have on a driver, and it often takes less than people think to be impaired.

To help make that point, right now law enforcement officers all across Washington are increasing enforcement of impaired driving, with a focus on poly-drug use. If part of your summertime activities involve substances that can impair your driving, make sure you have a plan that keeps you out of the driver’s seat.

Road Rules is a regular column on road laws, safe driving habits and general police practices. Doug Dahl is the Target Zero Manager for the Whatcom County Traffic Safety Task Force. Target Zero is Washington’s vision to reduce traffic fatalities and serious injuries to zero by 2030. For more traffic safety information visit Ask a question.