Skip to Content

Roadside drug detection


With the legalization or decriminalization of more recreational drugs, alcohol is no longer the only substance that police need to recognize. For years, police have used blood alcohol content as a reliable indicator of intoxication. Yet methods for detecting whether a driver is under the influence are not a straightforward as the breath test. 

Many drivers are now wondering how authorities tell if a driver is under the influence of a substance other than alcohol. In fact, 70% of Americans do not believe there would be any consequence for driving under the influence of a drug like cannabis. Additionally, more of the drivers surveyed approved of driving after using a substance like cannabis than driving drunk. The law, however, is clear that driving impaired has serious consequences. 

Drug testing methods 

A major concern for roadside drug detection is the recency of the drug use. Unlike alcohol, many drugs leave trace indicators in the user’s body long after the intoxicating effects have worn off. Police then have the problem of knowing whether the drug is still impairing the driver or if the trace amount is from previous use. 

Roadside saliva tests exist for drug impairment, but they are not perfect. Some tests indicate that cold weather affects the results. False positives and negatives are common according to a study from the Journal of Analytical Toxicology. The device has a 14.5% chance of identifying a false positive for marijuana and an 87.1% chance of showing a false positive for cocaine. A few states, including New York, continue to test these methods. 

Judging “impairment” 

Without firm numerical testing methods, police must judge driver impairment for themselves. Common indicators of intoxication include: 

  • Slurred speech 
  • Red or bloodshot eyes 
  • Poor coordination 
  • Panic or anxiety 
  • Slow reaction times 

Increasingly, police officers receive training to identify an intoxicated driver, but it is still a subjective measure in many instances.