Can Interlock Devices Detect Drugs?

Alcohol-impaired driving still remains a prominent issue in the United States, accounting for about 29 traffic-related deaths every day. However, drug-impaired driving is becoming another growing problem. Studies show that drugs other than alcohol are involved in about 16 percent of all motor vehicle crashes. The National Highway Traffic Safety Administration identifies and tracks over 400 different drugs that can cause impairment.

One of the most widely used tools in the fight against drunk driving is ignition interlock devices. As effective as they are, can interlock devices detect drugs? Read on to learn more.

What is an Ignition Interlock Device?

Car breathalyzers, or ignition interlock devices, connect to your car’s ignition and require you to blow into a mouthpiece before you can start your car. The mouthpiece connects to the device, which measures your blood alcohol concentration. If your blood alcohol concentration exceeds the limit set by the court, the IID will prevent you from starting your car for either a set amount of time or until you provide a clean breath sample.

In order to prevent samples taken from other people, most ignition interlock devices will also require you to periodically provide a breath sample while you drive, which is known as a rolling retest. If your BAC is over the limit, the device will log the event and sound an alarm until you shut off the engine or provide a clean sample.

Ignition Interlock Devices and Breath

Alcohol is not immediately metabolized as soon as you take a drink, nor does its chemical structure go through any changes, leaving it fairly intact as it enters your bloodstream. When your blood flows over and around your lungs, some of the alcohol actually evaporates into the alveoli, which are small sacs found throughout your lungs. When you breathe out, a breathalyzer or ignition interlock device can detect the alcohol in your lungs and provide a relatively accurate estimate of your blood alcohol level. The ratio of alcohol in your breath to alcohol in your blood is about 2,100 to 1, meaning that 2,100 milliliters of breath will contain the same concentration of alcohol as 1 milliliter of blood.

So, Can Interlock Devices Detect Drugs?

As they current are, ignition interlock devices are not capable of detecting drugs in your system, and it’s not as simple as tweaking the design of existing devices. All substances are metabolized differently and at different rates.

The main mechanism in action here is vapor pressure. Vapor pressure describes the behavior of a compound as it goes from liquid to gas Alcohol has a higher vapor pressure, meaning that its molecules are always escaping in gas form, which is why even without a breathalyzer or ignition interlock device, you can smell alcohol on a person very easily.

THC, CBD, and most other cannabinoids (the active components in marijuana) have low vapor pressures. If you were to try to measure THC the same way you measured alcohol, the process would take exponentially longer, and it wouldn’t be particularly accurate either. Currently, the only ways to accurately measure marijuana in a person’s system is through blood or urine samples.

Recent developments in science have developed a device that can detect marijuana, meth, and cocaine through someone’s breath. The problem is that researchers were unable to detect exactly when a person took a drug, which is a significant part of determining a person’s level of impairment. Some opioids, including THC, can stay in your body for weeks, meaning that you could be well past the point of impairment. This is compounded by the fact that some opioids are time released, while others are immediate release.

Drug-Impaired Driving Laws

Even though your ignition interlock device may not detect drugs just yet, it’s never a good idea to drive while drug-impaired. Aside from putting you and others on the road in danger, the potential punishments and penalties that you may incur if you’re caught could be substantial. Every state currently has laws for drug-impaired driving, though these laws vary from state to state and remain nuanced and hard to prosecute or enforce. While a breathalyzer or IID may not be able to detect drugs in your system, a police officer can still apprehend and arrest you if they believe you to be driving under the influence of a controlled substance.

It’s never a good idea to try to cheat your IID, which can result in harsher penalties and longer IID periods.

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