TUESDAY, May 10, 2016 (HealthDay News) -- The number of fatal car crashes involving marijuana more than doubled after Washington state legalized the sale of the drug, a new study finds.
Marijuana became legal in Washington in December 2012, researchers said. Between 2013 and 2014, the percentage of drivers in Washington involved in fatal car accidents after using marijuana rose from 8 percent to 17 percent, according to the study from the AAA Foundation for Traffic Safety.
In 2014 alone, one in six drivers involved in a deadly crash had recently used the drug, researchers found.
"The significant increase in fatal crashes involving marijuana is alarming," Peter Kissinger, president of the AAA Foundation for Traffic Safety, said in an AAA news release.
"Washington serves as an eye-opening case study for what other states may experience with road safety after legalizing the drug," he added.
At least 20 states are currently considering marijuana legalization, the researchers said. Washington, Alaska, Colorado, Oregon and Washington, D.C., have already legalized the recreational use of the drug.
The drug has also been legalized for therapeutic and medicinal use in 20 states, researchers said.
Whether or not marijuana is legal, no one should drive under the influence of the drug, the researchers noted. But it's not yet exactly clear how lawmakers should address the issue.
One problem is that the effects of marijuana vary from one person to the next. This makes the development of consistent and fair guidelines on safe legal limits very difficult, the researchers explained.
In order to control drug-impaired driving, some states have established legal limits for the drug.
These rules specify the highest level of active THC -- the main component of marijuana -- that drivers can legally have in their system. Active THC in the bloodstream typically suggests that someone has recently used marijuana, study authors said. THC affects the mind and can impair people's ability to drive safely, the researchers noted.
Montana and Washington state have implemented a legal limit for marijuana at 5 nanograms per milliliter (ng/mL). In Colorado, a blood concentration of at least 5 ng/mL means it's likely someone was driving under the influence of the drug, the researchers said.
Meanwhile, Nevada and Ohio have set a limit at 2 ng/mL. Pennsylvania's legal limit is lower at 1 ng/mL.
Twelve states have strict legal limits that prohibit the presence of any levels of marijuana in drivers' blood, the study authors said.
After investigating the lab results of drivers arrested for impaired driving, the researchers found many problems with legal limits for marijuana, including:
- There is no reliable scientific evidence that drivers become impaired when they have a specific level of marijuana in the blood.
- Various levels of marijuana have different effects from one person to the next. For some people, low THC levels may lead to impairment. Other people, however, may not be impaired even with high levels of marijuana in their system.
- Marijuana in the blood may drop to a legal limit before a suspected impaired driver is tested. On average, it takes more than two hours to take blood from a driver since it requires a warrant and people must be transported to a lab for testing.
"There is understandably a strong desire by both lawmakers and the public to create legal limits for marijuana impairment, in the same manner as we do with alcohol," said Marshall Doney, AAA's president and CEO.
"In the case of marijuana, this approach is flawed and not supported by scientific research. It's simply not possible today to determine whether a driver is impaired based solely on the amount of the drug in their body," Doney said.
Rather than rely on limits of THC in the blood, AAA advised states to use a two-pronged approach to enforce drug-impaired driving. This approach would include:
- A positive test for recent marijuana use.
- Behavioral or physiological signs that a driver is impaired.
The researchers noted this approach would rely heavily on law-enforcement training programs that help officers recognize drug-impaired driving.
"Marijuana can affect driver safety by impairing vehicle control and judgment," said Doney. "States need consistent, strong and fair enforcement measures to ensure that the increased use of marijuana does not impact road safety."
The U.S. National Institute on Drug Abuse provides more information on the effects of marijuana on driving ability.