Does Legal Pot Make Roads Less Safe?

States struggle to set scientifically valid standards, while fatal crashes involving drivers who recently used marijuana doubles.

At least 20 states could pass laws this year legalizing medical or recreational marijuana use. As many as 11 states will vote on marijuana on ballot measure in this fall's election.

While legalizing marijuana will almost certainly decrease the number of nonviolent offenders held in custody by law enforcement, legal pot presents a new challenge for authorities in the form of impaired drivers under the influence of marijuana.

But current legal limits for marijuana imposed on motorists are arbitrary and unscientific, according to research by the AAA Foundation for Traffic Safety. Because law enforcement agencies are operating under a flawed framework, innocent individuals could potentially be wrongly convicted of impaired driving while genuinely unsafe motorists go free.

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The study also found that fatal car accidents involving marijuana more than doubled once cannabis became legal within a state, suggesting an urgency to create a standard to measure drug-impaired driving.

While many states where marijuana is illegal have zero tolerance policies, six states, Colorado, Montana, Nevada, Ohio, Pennsylvania and Washington, set limits for THC, the psychoactive chemical found in cannabis, for impaired driving. The regulations mirror legal limits established for blood alcohol content (BAC) levels.

Though both are held to a similar standard, marijuana and alcohol are two entirely different substances. No research has reliably pinned down how high THC levels need to be to cause impairment, the AAA notes. Crash risk with higher BAC level is scientifically supported.

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Marijuana also isn't metabolized like alcohol. THC can linger in the bloodstream for days or weeks after a driver has used, so a suspected offender could be beyond the legal limit long after he or she has used marijuana. A 2013 study published in the journal Clinical Chemistry found that THC levels are still detectable in the blood of heavy smokers even after a month-long abstinence.

The rise in fatal car accidents in Washington after marijuana only reinforces the need for drug-driving enforcement. Between 2013 and 2014, the percentage of drivers who recently used marijuana in such accidents jumped 8 to 17 percent, though the study authors caution that these drivers were not necessarily impaired or at fault for the crash.

"Marijuana can affect driver safety by impairing vehicle control and judgment," Marshall Doney, President and CEO of AAA, said in a statement. "States need consistent, strong and fair enforcement measures to ensure that the increased use of marijuana does not impact road safety."

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Previous research has shown that drivers who test positive for marijuana are more likely to be involved in accidents. A 2011 Columbia University study found that motorists who either test positive or report driving within three hours of using were more than twice as likely as other drivers to be involved in car crashes.

As with any major public policy shift, getting used to legal marijuana will require both law enforcement and ordinary citizens to adapt. Even if the science isn't in on just who exactly is "too high to drive," using a drug and then getting behind the wheel is a bad idea whether marijuana is legal or not.

Medical marijuana gets all the headlines, but many legal weeds have traditions as medicines too. Although homeowners often consider these plants as lawn outlaws, weeds can serve as a floral pharmacy. However, would-be patients of the plants should consult a doctor before self-medicating.


Cichorium intybus, the light blue flower frequently seen along roads, provides the main commercial source of the compound inulin. Patients take inulin to fight high blood fats, including cholesterol and triglycerides, according to WebMD. Research published in Diabetes & Metabolism Journal suggests that inulin intake benefits women with type-2 diabetes by reducing the rate of blood sugar increase after eating. Inulin promotes the growth of certain bacteria in the intestines. While some believe this can help digestion, others suffer serious flatulence when the inulin-fed bacteria build up.

Some people add the dried and roasted root to coffee. Chickory coffee is especially popular in New Orleans.

Red Clover

Trifolium pratense contains chemicals known as isoflavones. These chemicals can act like the female hormone estrogen in the body. Doctors have examined the clover chemicals as a treatment for hot flashes and other symptoms of menopause. However, doctors warn that women with a history or risk of breast cancer should avoid isoflavones, since estrogen-like chemicals have been associated with increased incidence of some cancers.

Milk Thistle

Silybum marianum has a 2,000 year history as a liver medicine. Modern research has looked at thistle extracts as a treatment for alcohol-induced liver damage. Substances in milk thistle, particularly the chemical silymarin, may protect the liver from damage after a person takes an overdose of other medications, including acetaminophen (Tylenol). Milk thistle may also be an antidote to poison from the deathcap mushroom (Amanita phalloides). Animal studies found that milk thistle completely counteracted the poison if given within 10 minutes of poisoning, according to the University of Maryland Medical Center.


Native Americans used the milkweed (Asclepias sp.) as a contraceptive, according to the U.S. Department of Agriculture. The milky, white sap that gives the plant its name served to remove warts. However, milkweeds also contain chemicals known as cardiac glycosides. These chemicals can cause severe illness in humans and livestock. Monarch butterfly caterpillars eat milkweed and build up high concentrations of glycosides, which makes the insects nasty tasting to predators.


Ancient Greeks and Romans used horsetail (Equisetum arvense) to stop bleeding, heal ulcers and wounds, and treat tuberculosis and kidney problems. My wife drinks horsetail tea to flush out her body’s system and help lose weight. The tea has a mildly bitter flavor, similar to chamomile. Research published in Ethnopharmacolgy found that horsetail tea increases urination which corroborates my wife’s contention that the plant is a diuretic, or a substance that increases urination. However, doctors recommend taking a multivitamin when drinking significant amounts of horesetail tea, because it can flush nutrients, such as vitamin B1, thiamin and potassium, out of one's system as well.


In the past, Europeans used remedies made from dandelion (Taraxacum sp.) roots, leaves and flowers to treat fever, boils, eye problems, diabetes, and diarrhea, according to the University of Maryland Medical Center. Practitioners of traditional Chinese medicine take dandelions for stomach ailments and breast problems, such as inflammation or lack of milk flow. Dandelion leaves taste similar to spinach and contains vitamins A, B, C, and D, along with iron, potassium, and zinc.

Stinging Nettle

Urtica dioica can put the hurt on an hiker in shorts, but historically the plant has served to treat aching muscles and joints, eczema, arthritis and gout. People still use the plant to treat joint pain, and some studies have suggested that the plant can treat arthritis. Another study found that capsules of dried stinging nettle may reduce the symptoms of hay fever. Europeans frequently use stinging nettle root to treat bladder problems. Boiled nettle makes a side dish similar to collared greens.

For those who brush alongside stinging nettle, a remedy to the sting is often found growing nearby. Applying crushed up dandelion, horsetail, Aloe vera, jewelweed or the leaf of a dock or lock plant can counter the acid in the sting.


Like many of the medicinal weeds in this list, purslane (Portulaca oleracea) also makes a healthy snack. The plant contains a high content of omega-3 fatty acids. I ate some that grew in my yard and found it was somewhat sour. A little bit was good, but too much would be overpowering in a salad. In traditional Chinese medicine, purslane treats genito-urinary tract infections. Research published in Phytomedicine found that the plant reduced problems with cognition in older mice.


Since the age of the ancient Greek doctors have used plantains (Plantago sp., the weed in sidewalk cracks, not the fruit) to speed wound healing. In the training manual Survival, Evasion and Recovery, the U.S. Department of Defense recommends plantain as a poultice on wounds or as a nutrient-rich tea to treat diarrhea.


Traditionally, healers use burdock (Arctium sp.) to clear toxins from the blood and increase urination, according to the University of Maryland Medical Center. The plant also is used to treat skin ailments, such as eczema, acne, and psoriasis. The leaves and roots of burdock are edible and contains inulin, like chicory, so they may aid digestion and/or cause a nasty case of flatulence. Burdock also contains high quantities of antioxidants that can prevent damage to cells.