For years, Americans have been aware of the tragic problems caused by alcohol impaired driving and the toll it takes on individuals, families and communities.

But many of us don’t realize that impaired driving is not just an alcohol problem—it’s drugs, too. And many people who are driving under the influence are our own kids. But it’s not just users who are at risk—it’s all of us, sharing the roads.

After alcohol, marijuana is the drug most often linked to drugged driving. Tests for detecting marijuana in drivers measure the level of delta-9-tetrahydrocannabinol (THC), marijuana’s active ingredient, in the blood.

In the 2013-2014 National Roadside Survey, 12.6 percent of drivers on weekend nights tested positive for THC. This was significantly higher than the 8.6 percent who tested positive in 2007 (Berning, 2015).

Many marijuana users—and those of us who drive on the same roads as they do—don’t understand the dangers of mixing marijuana and driving.