Since Massachusetts voters passed a ballot initiative last month to legalize marijuana, lawmakers have grappled with a series of new issues, such as how to keep people from driving while stoned. UMass Boston psychology professor Michael Milburn, a Newton resident, believes his new mobile app provides a solution.

Police can use a Breathalyzer to measure the blood alcohol content of a person suspected of driving while drunk, but there’s no equivalent established device to measure how impaired a pot smoker is.

“A couple years ago, when it looked like marijuana legalization would be on the ballot in 2016, I started seeing stories that there’s no way to measure marijuana impairment,” said Milburn, who’s been teaching at UMass Boston for 39 years. “I have spent my career focusing on research, design, statistics and measurement. It occurred to me, I know how you could do that.”

Milburn’s app, DRUID, does not measure levels of intoxicants in a person’s system. Instead, the focus is on measuring and quantifying impairment. The app uses a series of cognitive and reflex-based tasks performed on a touch screen to calculate an impairment score. The app tests reaction time, decision making, motor tracking, balance and ability to measure time.

While lawmakers have set the legal blood alcohol content at 0.08 percent, setting a similar threshold for THC, the psychoactive chemical in marijuana, presents challenges. A person’s THC level makes can be measured by analyzing a blood sample, but many researchers say THC blood content isn’t a good measure of impairment. Since THC is fat-soluble, it remains in the body for weeks, long after a pot-smoker’s high has worn off.

Colorado and Washington state have laws that set a 5 nanogram per milliliter legal impairment threshold for THC content, an approach Milburn calls misguided.

It remains to be seen what approach Massachusetts lawmakers will take. The issue of drugged driving is something lawmakers have said they need to address.

“We’re putting the public at risk,” state Sen. Vinny deMacedo, R-Plymouth, said in an interview shortly after Election Day. “We do not have a test for people driving under the influence of marijuana.”

The AAA Foundation for Traffic Safety conducted a recent study that found the number of drivers in Washington state who tested positive for THC in post-crash blood tests increased from 20 percent to 30 percent from 2005 to 2014. The state legalized recreational marijuana use in 2012.

The DRUID app, which costs 99 cents, is currently available for the Apple iPad. An iPhone version is in development, and Milburn hopes to also release Android versions.

In addition to measuring impairment, the app can also be used to anonymously collect data, helping app developers produce more accurate testing results and learn more about the effects of marijuana intoxication.

For now, the app is intended for personal use by pot smokers who want to avoid driving while impaired. Milburn hopes the tool could one day also be used by law enforcement.

“I think it’s important for the legislature to avoid passing bad laws related to marijuana, like a 5 nanogram per milliliter THC level,” Milburn said. “Massachusetts needs to get ahead of the curve and recognize this kind of instrument is going to be more effective and produce fairer outcomes.”