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Drugged driving and roadside stops: Is there a valid portable test?

On Behalf of | Mar 7, 2016 | DUI

Yes, alcohol is a drug. But there’s a big difference between drunk driving and drugged driving in terms of the capacity of chemical tests to show impairment.

For drunk driving, there is a clearly accepted chemical test for impairment, based on the 08 blood-alcohol content limit. For drugged driving, there is no such clearly accepted limit. The same is true in cases where someone is under the combined influence of alcohol and drugs.

In this post, we will explain how and why this is so. We will also apply that reasoning to Kentucky’s recent experimentation with roadside drug tests.

The .08 standard

The .08 standard for drunk driving has been the legal limit for blood-alcohol content in Kentucky and across the country for many years now. It is the result of many years of research into the effect of alcohol consumption upon the ability to drive a motor vehicle safely.

Researchers have learned that alcohol spreads throughout the body’s systems evenly. Measuring the volume in the breath or blood (or even urine) can be used to infer how much alcohol was affecting the brain.

This type of simple equation is not possible for drugs other than alcohol or for impairment that is due to a combination of drugs and alcohol. In particular, as NPR reported last month, it is not possible to easily infer impaired driving from marijuana based on THC levels.

THC levels

THC is the active chemical ingredient in marijuana. Unlike alcohol, THC is soluble in fatty tissue – such as brain tissue. THC that has been absorbed in brain tissue therefore may not correspond with THC in the blood.

Indeed, researchers have even found that THC can leach out of the brain and back into the blood in occasional marijuana users. In practice, this means that a drug test does not necessarily show an accurate amount of THC that is actually affecting the brain at a given time.

There are also differences between eating and smoking weed in terms of the test results. Oral consumption of cannabis produces lower THC levels than smoking. Another complicating factor is that frequent smoking of cannabis can cause prolonger changes in brain chemistry that last for up to several weeks after marijuana consumption.

Our point is that, for driving impaired by marijuana, there is no obvious indicator of intoxication as there is for alcohol. Recent research has shown the scientific basis for the difference between the two substances.

New roadside drug tests in Kentucky

It is hard to reconcile the research on THC levels with Kentucky’s recent experiments with roadside drug tests for drugged driving. The state’s Office of Highway Safety is collaborating with local officials in three counties to have officers try out portable test kits for drugged driving.

The kits would analyze saliva samples for as many as 10 drugs. When the tests were first rolled out in the three collaborating counties, they were given only to volunteers who had already been arrested. But eventually the tests could become a tool that officers could use in making arrest decisions.

The question, however, is whether roadside drug tests are really based on sound science.

If you are stopped for impaired driving, it’s important to protect your legal rights with help from a skilled attorney. You don’t want law enforcement authorities to get away with using questionable roadside tests against you.