How can the Police Prove Impairment in DUI Marijuana Cases?

Driving under the influence of marijuana is becoming more common as laws relax around cannabis use. But how can police actually prove you’re impaired and unsafe behind the wheel if you’ve smoked some weed? It’s not as straightforward as testing blood alcohol levels. Let’s break it down.

Observing Driving Behavior

Most DUI arrests start with the police pulling someone over for erratic driving – weaving between lanes, running stop signs, etc. Even if the driver doesn’t seem wasted, the way they were operating the vehicle can be the first sign of impairment and probable cause for the officer to investigate further.

Interacting with the Driver

Once pulled over, the officer will speak to the driver and passenger(s) if there are any. They’ll ask questions about where the driver is coming from, where they are going, if they’ve had anything to drink, etc. The driver’s speech, coordination, and inability to follow instructions can all be evidence of intoxication from marijuana or other drugs.

Smell

One of the most obvious signs is the distinctive smell of pot coming from the car or driver’s breath and clothes. While the odor alone isn’t enough to prove DUI, it gives weight to the officer’s suspicions.

Field Sobriety Tests

The standard roadside tests like walking a straight line and standing on one leg can indicate impairment, but aren’t as definitive as with alcohol. Since marijuana affects people differently, poor performance doesn’t always mean the driver is unsafe. Refusing the voluntary tests can’t be held against you in court.

Drug Recognition Experts

Some jurisdictions call in special Drug Recognition Experts (DREs) to examine weed DUI suspects back at the station. They check vital signs, pupil size, muscle tone and conduct multiple sobriety tests to determine if the driver is impaired and by what substance.

Chemical Testing

Unlike a breathalyzer for alcohol, there’s no roadside device to test for marijuana. Police usually rely on blood tests to measure the level of THC and its metabolites. However, many factors make it hard to correlate the results with impairment. For one, THC can be detected long after the effects wear off. And frequent users can have high THC blood levels while still driving safely.

It’s Complicated

So in summary, while cops have tools to build a DUI case, it’s not as simple as with drunk driving. Defense lawyers can often successfully fight marijuana DUIs by picking apart the evidence and lack of definitive impairment proof.

Some key strategies include:

• Challenging the reason for the initial stop if driving wasn’t clearly reckless
• Disputing the officer’s subjective observations during questioning and sobriety tests
• Casting doubt on the relevance of blood THC levels
• Pointing out flaws in the DRE’s investigation and conclusions

It’s an evolving area of law and science, but beatable charges if you have an experienced DUI defense attorney on your side.