The scent of marijuana has become common on Long Island’s highways, and as lawmakers in Albany finalize plans to legalize adult recreational use of the drug, that should concern all of us, especially given our suburban reliance on cars.

Suffolk County already leads New York State in fatal automobile crashes, including those involving alcohol, and according to National Highway Traffic Safety Administration data, Nassau isn’t far behind. To what extent legalizing recreational marijuana leads to more car crashes or traffic deaths remains unclear. Published studies in states such as Colorado and Washington that greenlighted weed sales a few years ago have been conflicting — in part, because testing positive for THC, the major psychoactive biochemical found in marijuana, doesn’t confirm impairment but only indicates its presence in the bloodstream that could date back several days.

We do know, however, that driving requires split-second multisensory decisions and is one of the most challenging and complex activities people engage in on a daily basis. Marijuana significantly impacts judgment, motor coordination and reaction time. Controlled studies using driving simulators have found a direct relationship between blood THC concentration and impaired driving ability.

Proving that roadside is another thing, and technology has lagged behind policy. Since 1954, police have used Breathalyzers to measure blood alcohol concentration (BAC), and 60 years’ worth of data helped pinpoint .08% as the legal limit in terms of alcohol impairment. When it comes to pot, law enforcement has little more than field sobriety tests and saliva swabs, both of which are frequently subject to legal objections.

Guiding cannabis consumers is challenging because several factors influence intoxication onset, intensity and duration, including the type of marijuana product consumed, how it’s ingested, its potency based on THC content, and user characteristics. Smoking often causes immediate intoxication, with impairment typically lasting a few hours, while the effect of edibles is usually delayed, but lasts longer.

Multiple studies have confirmed that driving under the influence of alcohol and cannabis simultaneously is riskier than driving after using either substance alone. Both drinkers and cannabis users also routinely underestimate their level of impairment, and many believe they actually drive better when stoned. That’s why New York needs to invest in a statewide multipronged driver safety public awareness campaign now, before pot store parking lots are packed.

New York’s cannabis program must include plans to better detect and combat marijuana-impaired driving, including devices capable of measuring marijuana levels in drivers and better data collection on the prevalence and impact of impaired driving.

Drunken driving crashes and fatalities in New York began to drop after the State Legislature enacted the Stop-DWI law in 1981, stiffening penalties for drunken driving and launching new prevention, enforcement and treatment programs funded with fines collected from offenders. The 2009 passage of Leandra’s Law, requiring ignition locks for convicted drivers and boosting the penalties for putting child passengers at risk, saved lives as well.

That’s why driving while impaired by marijuana must remain a misdemeanor and impaired driving crimes must be charged based on the condition of the driver, not whether the substance can be named and is on the state’s legal list of drugs. Clear legal definitions advance, rather than contravene social justice, especially if we consider losing a loved one at the hands of an impaired driver the ultimate injustice.

Jeffrey L. Reynolds is president and CEO of Family & Children’s Association, which provides addiction treatment and mental health services on Long Island.