A new study has found that more than half of teen and young adult drivers who lost their lives in car crashes had pot and/or alcohol in their system at the time.

Katherine Keyes of Columbia University's Mailman School of Public Health led the research project, which analyzed the data of 16- to 25-year-olds from the Fatality Analysis Reporting System (FARS), a federal database of fatal crashes. Keyes and her colleagues focused on the nine states that test roughly 85% of its car crash victims for drugs and alcohol within an hour of the incident, including California, Illinois, and Rhode Island.

They concluded that 50.3% of those young drivers who passed away had marijuana, alcohol, or both in their system at the time. About 36.8% of those who lost their lives had alcohol alone in their systems, 5.9% tested positive for marijuana alone and 7.6% had been using both.

“Given the rapid changes currently underway in marijuana availability and permissibility in the U.S., understanding the effects of drug control policies on substance use behavior and adverse health outcomes, such as fatal motor vehicle crashes, has never been more important," said Keyes.

The age of those involved in the fatal car crashes also played a role in the substances found in their system. Keyes and her team found that the likelihood of finding alcohol alone in the crash victims’ systems went up by 14% once they reached age 21, while the likelihood of finding pot alone went down 24%. But perhaps surprisingly, the chances of finding both marijuana and alcohol in the crash victims’ systems was 22% higher when the victim was over the age of 21.

"Taken together, we found no significant substitution effect between alcohol and marijuana," said study researcher Guohua Li, director of Columbia University's Center for Injury Epidemiology and Prevention. "Rather, increased availability seems to increase the prevalence of concurrent use of alcohol and marijuana."

The results of this study were similar to findings from other recent research projects. A 2012 study published in the journal Addiction found that 57.3% of drivers ages 18-25 who died in fatal car crashes had some kind of mind-altering substance in their system. Alcohol was the most prevalent substance in these instances.