Drugged driving is difficult to detect, but it impairs drivers and contributes to accidents and fatalities

Cannabis slows reaction time and alters spatial awareness. 
 (Jason Doiy, iStock, Getty Images via The Conversation CC)

Despite its often invisible presence, drugged driving is a developing problem in most states. On rural roads where almost half of fatal crashes in the U.S. occur, the risks posed by drugged drivers may be disproportionately higher, but difficult to detect or prove.

In 2020, roughly 12.6 million people aged 16 and up drove after using illegal drugs. "Of that total, roughly 11.7 million were under the influence of cannabis," writes Andrew Yockey, a public health expert at the University of Mississippi, for The Conversation. 

While cannabis use is often downplayed, it impairs reaction time and spatial perception. Yockey explains, "Multiple studies have found that drivers with THC, the primary psychoactive compound in cannabis, in their bloodstream are about twice as likely to be involved in a fatal crash – either as the cause or as a victim – compared with those who haven’t used drugs or alcohol."

Other drugs or any mix of drugs also play a part in devastating vehicle collisions and fatalities. "Opioids can cause drowsiness and dizziness. Stimulants like cocaine or methamphetamine may lead to overconfidence and aggressive driving," Yockey adds. "When drugs are mixed — or combined with alcohol — the risks increase dramatically."

All states prohibit drugged driving, but how they enforce those laws varies, leaving "legal gray areas in how the laws are interpreted and enforced," Yockey writes.

Despite laws designed to discourage and punish drugged driving, detecting and measuring illicit drug use in drivers is tricky. "There is no standardized way to measure drug impairment as there is with blood alcohol content," Yockey explains. "Roadside tests that cops use to spot drunk drivers don’t work as well for drug impairment."

States have increasingly turned to using roadside saliva tests, which can "detect recent drug use more quickly," Yockey writes. But again, the measurement of drugs still in the bloodstream and how that translates into driving impairment or ticketed offenses isn't clear.