A survey from the National Highway Traffic Safety Administration has revealed some good news and some bad news for American motorists. First, the good news: Drunk driving is decreasing nationwide. The bad news? Drugged driving may be replacing it in popularity.

According to the NHTSA’s poll, the frequency of driving under the influence of alcohol seems to be decreasing. The survey examined 9,000 American drivers from 300 locations during the weekend evening hours. Approximately 1.5 percent of drivers had blood alcohol concentrations above the legal limit–a 0.7 percent decrease from ten years ago. However, a whopping 20 percent had illegal drugs in their system, up from 16.3 percent in 2007.

Harsh penalties for drunk driving and widespread public awareness  may partially account for the decrease in drunk drivers. Many states have implemented strict penalties for motorists caught driving under the influence of alcohol. There have also been several major public awareness campaigns against driving while intoxicated–for example, Massachusetts’s “Drive Sober or Get Pulled Over” campaign.

Finding an explanation for the increase in drugged driving may be more complex. One reason may be the increased access to marijuana that accompanied several states’ recent decriminalization of the drug. It could be that residents are more likely to drive under the influence of pot when they have easier access to it. To combat this, Colorado and Washington–two of the states that legalized recreational marijuana–have set a legal limit on how much THC drivers are allowed to have in their system. If drugged driving continues to increase nationwide, more states may impose legal limits as well. Currently, law enforcement tends to use blood tests, mouth swabs and even breathalyzers to test for the presence of illegal drugs. Drivers who are caught with illegal drugs in their system may be charged with an OUI and face fines, license revocations or even jail time.