Researchers at Washington State University are working on a handheld breathalyzer that could detect if a driver tests positive for marijuana use.

Although it's legal for people to smoke marijuana recreationally and for medical reasons in four states (Washington, Alaska, Colorado and Oregon), users are not allowed to get behind the wheel if they have more than five nanograms of THC (an active ingredient found in cannabis) per milliliter of blood.

A similar tool to breathalyzers that are used to prevent drunk driving could work for cannabis users. As of now, determining sobriety after smoking typically involves a blood test, the results of which can take up to a day to come in.

WSU chemistry professor Herbert Hill and doctoral student Jessica Tufariello are developing a tool that would give police an immediate way to detect whether THC is present in the driver's blood stream (but won't yet tell exactly how much), The News Tribune first reported.

Driving under the influence of marijuana is an increasing concern in the states that legalized the drug. About 25% of blood samples taken from stopped drivers in Washington state in 2013 tested positive for pot, according to the Seattle Times.

There has been no significant increase in car accidents as a result, but police can still arrest drivers who are under the influence. The Colorado Department of Transportation's website states that "getting high and getting behind the wheel of a car will get you arrested for a DUI — this law hasn’t changed with the legalization of marijuana in January 2014."

"Marijuana affects reaction time, short-term memory, hand-eye coordination, concentration and perception of time and distance," the website continues.

This isn't the first time a product intended to keep marijuana-influenced drivers off the road has introduced. Earlier this month, a breathalyzer called Cannabix, which also detects THC in one's system, was revealed at the National Marijuana Business Conference in Las Vegas. Cannabix is slated to roll out first to law enforcement and businesses, then to consumers; it is scheduled to hit the market next year.

The name and release date of Washington State University's breathalyzer are currently unknown.

BONUS: The History of Marijuana in the United States