Atlanta, GA- A new study of fatally injured drivers shows that the number of drivers testing positive for marijuana and other drugs steadily increased between 1999 and 2010, indicating that marijuana and other drugs are playing a larger role in fatal traffic collisions.

The study was conducted by researchers at Columbia University’s Mailman School of Public Health who analyzed data from the National Highway Traffic and Safety Administration’s Fatality Analysis Reporting System. Of the 23,591 drivers who died within an hour of their crash 39.7 percent tested positive for alcohol and 24.8 percent tested positive for other drugs.

Drug use among drivers in fatal accidents rose from 16.6 percent in 1999 to 28.3 percent in 2010, according to Science Blog. The most commonly detected drug used by drivers was marijuana, which increased from 4.2 percent to 12.2 percent.

Researchers noted that alcohol use remained stable during the study period. Men made up 46.1 percent of alcohol-related fatalities while women made up 26.1 percent. While alcohol use remained stable for both sexes, drug-related fatalities rose sharply for both sexes in all age groups.

“Although earlier research showed that drug use is associated with impaired driving performance and increased crash risk, trends in narcotic involvement in driver fatalities have been understudied,” said Guohua Li, MD, DrPH, professor of Epidemiology and Anesthesiology and director of the Center for Injury Epidemiology and Prevention. “Given the increasing availability of marijuana and the ongoing opioid overdose epidemic, understanding the role of controlled substances in motor vehicle crashes is of significant public health importance.”

Joanne Brady, a PhD candidate in epidemiology and the lead author of the study, pinpointed decriminalization of marijuana in 20 states plus Washington D.C. as one of the reasons drug-involved fatalities have increased.

“Although each of these states has laws that prohibit driving under the influence of marijuana, it is still conceivable that its decriminalization may result in increases in crashes involving marijuana,” Brady explained to Science Blog.

Researchers pointed out that their data only comes from six states that require toxicology tests for drivers who are involved in fatal crashes– California, Hawaii, Illinois, New Hampshire, Rhode Island, and West Virginia.

They also noted that different drugs have different effects on driver’s skills and ability to react in an emergency situation. The researchers also pointed out that marijuana can be detected in a person’s system days after the intoxicating effects have worn off.

The study, which was published in the Journal of Epidemiology, did not however clarify if the drivers who tested positive for drug use also hade alcohol in their systems at the time of their crash. To blame the increased of drug-related fatalities solely on marijuana seems short sighted, and it would be pertinent to determine how many intoxicated drivers tested positive for prescription drugs.

As the researchers noted, each drug has different effects on a driver and a DUI attorney can challenge the charges by questioning whether their clients was actually impaired at the time of their arrest.