Tens of millions of drivers face the prospect of a breathalyzer test for weed in the coming years in the U.S. as the trend toward medical marijuana legalization and outright adult-use legalization collides with another trend: the decades-old push to make the roads safer.

The much-feared breathalyzer for weed isn’t going to rely on breathing, however, it’s going to use spit. And when combined with unjust, new “zero tolerance” laws, futuristic roadside THC tests promise to pick up where the old fashioned drug war left off.

Road Carnage

Roughly 33,561 people died in traffic collisions in America in 2012, and doctors admitted about 2.3 million adults into emergency rooms for traffic-related accidents in 2009, the CDC reports. Traffic collisions are the leading cause of death for U.S. teens, and this is after a decades-long campaign to bring the number of injuries and deaths down.

That campaign has been successful. Traffic fatalities are at historic lows, arguably through the use of tough seatbelt laws and drunk driving laws combined with checkpoints and saturation patrols around holidays.

Driving Under the Influence investigations begin with such checkpoints, or a roadside stop for an infraction of some kind. If an officer suspects DUI, he or she will administer a motor skills test, and in the case of alcohol, an alcohol detection screening commonly dubbed a ‘breathalyzer’.

The portable handheld device gives officers a basic idea of a person’s blood alcohol content and anything over .08 is a “per se” DUI, meaning it doesn’t matter if you don’t feel or act drunk, legally you are considered drunk. Failing a breathalyzer test will lead to your arrest and urine or blood testing back at the station, which is used in a defendant’s trial, notes California attorney Omar Figueroa.

For weed, things are different. In California, it’s illegal to drive high on any drug, but there is no “per se” limit set for weed. (Scientifically, the amount of marijuana compounds in a person’s system does not correlate to impairment.) So if an officer thinks you’re high, they can give you a skills test, but there’s no breathalyzer stage to back up what an officer suspects. Drivers suspected of a marijuana DUI have to be cuffed and taken in for a urine or blood draw, which takes time and money, so it’s often reserved for serious injury collisions.

But many think that’s about to change.

Sudden Gasps

In August, Baltimore research Sarah Himes published a study in the Journal of Breath Research that caught fire. She collected exhaled breath from 24 smokers and non-smokers using breath pads and tested them for THC, the main active ingredient in marijuana. Sure enough, she could tell who had just smoked a joint and who hadn’t.

“Breath may offer an alternative matrix for testing for recent driving under the influence of cannabis, but is limited to a short detection time (0.5-2 h),” the paper concludes.

Huffington Post, Mother Jones and others jumped on the story, despite that fact that the science behind testing breath for THC goes back to at least 1982. The method is also totally impractical in the field, where untrained officers need to rapidly assay the presence and concentration of pot in a driver’s system.

A company called SenseAbuse also made waves in 2013 after the press billed it as a breathalyzer for marijuana. Again, subjects had to exhale into a cartridge which had to be sent off to a lab for analysis. That can take weeks, so it’s not a real breathalyzer.

Some Cheek

While many are wringing their hands about a theoretical study and an impractical device, drivers are going to jail for failing a roadside THC screen — just overseas. The Europeans are years ahead of the U.S. on road safety — with novel new kits for detecting the presence of marijuana and other drugs, combined with stiff zero tolerance “per se” laws to send sober smokers to jail.

The Italian paper Ansa reports Nov. 11 that Italian police are using a drug test kit called the “DrugWipe 5 S”, which involves swabbing the saliva of a suspect instead of analyzing their breath. Two motorists were busted on the side of the road after a DrugWipe detected THC in their spit.

The DrugWipe 5 beat out eight other on-site oral fluid screening devices in a four-year, multi-country trial called DRUID in Europe which concluded in 2010.

“To date, oral fluid screening devices for the detection of drugs have been used in only a few countries, but an increasing number are planning to introduce them as a legal screening device,” DRUID researchers write. “The benefits of using oral fluid for drug screening purposes is that recent drug use can better be detected in oral fluid than in urine, sweat or hair. On top of that, oral fluid collection is much less invasive than urine collection.”

Zero Tolerance

Europe’s zero tolerance “per se” drug laws have become all the rage in U.S. law enforcement circles, notes California attorney Omar Figueroa. Fourteen states, predominantly in the Midwest, will lock you up if you’re sober, but still have any byproducts of marijuana in your system.

For example, under the Arizona per se law, a regular weed user is technically DUI in Arizona for up to a month after he or she quits. Every year Californians must beat back copycat laws calling for zero tolerance “per se” limits on marijuana that are promulgated by police lobbies, notes Paul Armentano, Deputy Director of NORML.

“Detecting THC is not the same as impairment,” he said. “I abhor the policy.”

“Per se” limits mean the government doesn’t have to prove you are high, he said. They are massively unjust, and a vindictive sheriff in a “per se” state – like Arizona – could easily buy and deploy a bunch of DrugWipes at DUI checkpoints near a college or a concert to generate DUIs, convictions and law enforcement income.

“What’s to stop Sheriff Joe Arpaio? Nothing,” Armentano said. “But it hasn’t happened yet.”

“I’m not really terribly concerned about any of these [kits], unless it’s misused like it is in Australia, where drivers and tested randomly on the road,” said Dale Gieringer, director of California NORML.

Wasting Money

Cost-benefit analyses don’t justify anything more than select deployment of THC cheek swabs, experts note.

“The time-consuming process of on-site oral fluid screening, in combination with the quite high cost of the devices and the relatively low sensitivity for cannabis, which in many countries is the most frequently used illegal drug, will probably prevent large-scale random drug testing in practice,” the DRUID report concludes.

A stoned driver is 1.83 times as likely to get in a crash as a sober one, but a drunk driver is 13.64 times as likely to be in a crash, writes researcher Guohua Li, a professor of epidemiology and anesthesiology and the founding director of the Center for Injury Epidemiology and Prevention at Columbia University, in a 2013 paper.

Other 2013 research from D. Mark Anderson from Montana State University shows legalizing pot makes roads significantly safer through substitution, meaning would-be drunk drivers are lighting up legal weed, drinking less, and staying home instead.

This article originally appeared in Culture Magazine.