At what point is someone too high to get behind the wheel? The answer is complicated. Brain scientists and pharmacologists don’t know how to measure if and to what extent marijuana causes impairment.

In an article by Kaiser Health News, an editorially independent program of the Kaiser Family Foundation sent to me by Craig Collette, Stop DWI coordinator for Franklin County, presents some interesting information that should be considered by our lawmakers, as Governor Cuomo said Dec. 17th that legalization would be a top priority for 2019. Marijuana is now legal for recreational use in 10 states and the District of Columbia. And nearly three dozen states allow the use of medical cannabis.

For alcohol, there is a clear, national standard. If your blood alcohol content (BAC) is 0.08 percent or higher, you’re considered cognitively impaired at a level that is unsafe to drive. Extensive research supports this determination, and the clarity makes enforcement of drunken driving laws easier. Setting a marijuana-related impairment level is a much murkier proposition. But states that have legalized pot and those proposing to, including New York, have to figure it out, say experts.

“You can’t legalize a substance and not have a coherent policy for controlling driving under the influence of that substance,” said Steven Davenport, an assistant policy researcher at the nonprofit Rand Corp., who specializes in marijuana research. Marijuana, after all, weakens a driver’s ability to maintain focus, and it slows reflexes. But regulators are “playing catch-up,” suggested Thomas Marcotte, a psychiatry professor at the University of California-San Diego and one of a number of academics around the country who is researching driving while high.

States have put forth a bevy of approaches. At least five have what’s called a “per se” law, which outlaws driving if someone’s blood level of tetrahydrocannabinol, or THC, exceeds a set amount. THC is marijuana’s main intoxicant. Colorado, where voters approved legalization of recreational marijuana in 2012, deems “intoxicated” any driver who tests higher than 5 nanograms of THC per milliliter of blood.

Rhode Island, Pennsylvania and Indiana are among states that forbid driving at any THC level. Still others say drivers should be penalized only if they are impaired by the chemical — a standard that sounds reasonable but quickly gets difficult to measure or even define. None of these approaches offers an ideal solution, experts say. “We’re still definitely evaluating which policies are the most effective,” said Ann Kitch, who tracks the marijuana and driving issue for the National Conference of State Legislatures.

States that set a THC-level standard confront weak technology and limited science. THC testing is imprecise at best, since the chemical can stay in someone’s bloodstream for weeks after it was ingested. Someone could legally smoke a joint and still have THC appear in blood or urine samples long after the high passes. There’s general agreement that driving while high is bad, but there’s no linear relationship between THC levels and degree of impairment.

In Canada, which legalized recreational pot last October, enforcement will test drivers with a saliva test called the Dräger Drug Test 5000, but that isn’t perfect either. Some private companies are trying to develop a sort of breathalyzer for marijuana, but it’s really hard to have an objective, easy-to-administer roadside test.

So, the dilemma continues. New York state lawmakers have a very difficult decision whether to legalize recreational marijuana before there is an easy to administer roadside test that will determine a definitive impairment amount of the drug. Hopefully solutions will be found sooner than later, but don’t hold your breath.