Medical or recreational marijuana and drugged driving.

Author:Larkin, Paul J., Jr.
Position::IV. The Framework for Addressing Marijuana-Induced Drugged Driving through Conclusion, with footnotes, p. 480-515

    1. The Existing Framework for Alcohol

      The principal federal law regulating the police response to driving while intoxicated is the Fourth Amendment. (110) Applicable to "searches" and "seizures" of a person or his property, (111) the Fourth Amendment permits a law enforcement officer to make a brief investigative stop of a vehicle if, based on the totality of circumstances, he has "a particularized and objective basis" for suspecting that the driver is intoxicated. (112) The reasonable suspicion standard is not exacting. A mere "hunch" is insufficient, (113) but the level of suspicion required is "considerably less" than proof of wrongdoing by a preponderance of the evidence," and is "obviously less" than the proof necessary for probable cause to arrest. (114) A police officer can rely on his own observations or those of a bystander, such as another driver, if the private party's reports are sufficiently reliable. (115) In assessing the evidence, police officers not only may reach common sense conclusions about human conduct, (116) but also may draw on their experience and training to make inferences from and deductions about the entire body of information available to them--inferences and deductions that "might well elude an untrained person." (117) Police officers also need not rule out the possibility of innocent conduct in order to make an investigatory stop. (118) Accordingly, if a police officer sees (or receives a reliable report) that a particular motorist is handling his vehicle in a manner suggesting that the driver is intoxicated--for example, if one car almost forces another automobile off the road--the officer is justified in stopping the driver in order to determine if he is under the influence of alcohol. (119)

      Once a police officer stops a driver suspected of being under the influence of alcohol, the officer then focuses on that person and his vehicle. There are several potential physiological signs of intoxication, such as the odor of alcohol on a person's breath, (120) slurred or garbled speech, bloodshot eyes, mydriasis (dilated pupils), unresponsiveness of the pupils to light, nystagmus (rapid involuntary eye movement), swaying or staggering when walking, aggression or a refusal to cooperate, and impaired balance or movement. (121)

      If a police officer concludes that the driver may be impaired by alcohol, the officer may require him to complete one or more informal sobriety tests, such as touching finger to finger or pronouncing "Methodist Episcopal" without a lisp. (122) Alternatively, the officer may administer a Standardized Field Sobriety Test, a test developed by the National Highway Traffic Safety Administration (NHTSA) as an objective, noninvasive, easily applied means that police officers can use at roadside to determine intoxication. (123) It requires a driver to walk in a straight line, turn around, and retrace his steps (Walk-and-Turn or WAT); to maintain his balance while standing on one foot (One-Leg Stand or OLS); and to watch a moving object (Horizontal Gaze Nystagmus or HGN). (124) If the driver cannot successfully perform the first two tasks or if his eyes saccade as he watches a moving object, the officer may conclude that he is inebriated. (125) The officer also can require the driver to submit to a breathalyzer test or temporarily forfeit his driver's license under many state "implied consent" laws. (126)

      Police officers have used breathalyzers on innumerable occasions since they first became available because they are portable, easily and quickly administered, noninvasive, and, perhaps most importantly, given the relatively simple pharmaceutics of alcohol, very reliable. (127) Moreover, the same ethyl alcohol is present in every alcoholic beverage; only the quantity and flavoring additives differ. (128) Breath testing is the standard means for measuring alcohol-induced intoxication because alcohol, a volatile liquid, is excreted (in part) through the lungs. (129) There also is an established straight-line correlation between the presence of a particular blood-alcohol level and the impairment it causes. (130) Breath testing therefore can be used in lieu of blood testing or a urinalysis test to detect the presence and debilitating effect of alcohol. (131) The result is that curbside or roadside breathalyzer tests permit law enforcement officers to police drunken driving in an effective, reliable, nondegrading manner. (132)

    2. The New Framework for Marijuana

      1. Treating Driving Under the Influence of Drugs in the Same Manner as Driving Under the Influence of Alcohol

        Over time, states added drugs such as marijuana to their reckless driving or DUI laws. (133) Unfortunately, there is no procedure comparable to the Standard Field Sobriety Test that a police officer can administer on a roadside to determine if a driver is under the influence of drugs. For example, marijuana diminishes a person's temporal and spatial judgment, but the Standard Field Sobriety Test does not measure those effects. (134) Police officers also rely on nystagmus to determine if a person is under the influence of alcohol, but drugs that dilate or constrict the pupils do not also cause nystagmus. (135) There also is no device comparable to a breathalyzer to identify marijuana intoxication or the presence and amount of THC, the psychoactive ingredient in marijuana, in a driver's blood. (136) What is worse, even if that measurement could be done, there is no medical or scientific consensus regarding the amount of THC that would impair the average driver. That is true for a host of reasons, most of which stem from the fact that the relevant pharmaceutics are far more complicated for drugs than for alcohol. (137)

        Alcohol has been the subject of extensive testing over decades. Science has established a strong relationship between BAC level and impairment or crash risk and that a person's B AC level changes slowly over time. (138) By contrast, there are a host of factors that affect how a given drug concentration affects someone. Individuals differ in their body weight and composition, absorption, distribution, metabolism, and accumulation of a drug, as well as the effect it may have due to the rate at which it is absorbed, the frequency by which it has been used, and whether the blood-concentration level was obtained when the amount of the drug consumed was rising or falling. (139) The effect of cannabis on an individual also hinges on what is known as "the set and setting" in which he uses marijuana--that is, an individual's prior experience with marijuana, his attitude toward its effect, his current mood, and the social setting in which it is used. (140) Moreover, there presently is a poor correlation between the level of a drug in a driver's blood or plasma and the effect of that drug on his psychomotor or executive functions, because there will be detectable levels of illicit drugs in a driver's system long after the impairing effect of the drug has worn off. (141) Also, some parties who repeatedly use certain drugs develop a tolerance to their neurocognitive effects, requiring users to increase their dose over time in order to obtain the same pleasurable effect, which means that the effect a drug may have on a driver's motor skills will vary from driver to driver. The upshot, as NHTSA concluded in 2009, is two-fold: First, testing for the presence of marijuana in a driver's system has not yet reached the same state of scientific knowledge that we possess today for BAC testing. Second, specific drug-concentration levels cannot be reliably equated with effects on a driver's performance. (142) Any particular level could be overinclusive or underinclusive. (143)

        Unfortunately, science has not moved the needle far since then. That is true for several reasons.

        Start with the fact that there is no study showing any residual, long-term effect of chronic marijuana use on a person's ability to drive, (144) nor is there evidence that THC remains in brain tissue on a long-term basis. (145) Long-term marijuana smokers are no more likely than non-smokers are to be involved in a vehicle accident unless they are actually intoxicated while driving. (146) Accordingly, it is critical to measure a driver's THC concentration relatively shortly after he uses marijuana because long-term measurements are not very helpful.

        A high THC concentration, however, is transient. THC concentration in blood peaks within minutes of smoking marijuana and elevated levels last up to an hour, but then rapidly decrease, even though functional impairment lags behind peak THC levels. (147) An individual therefore can be far more "stoned" in fact than his THC test results would indicate. At the same time, if a person has a high drug tolerance level, "there is often no difference in psychomotor performance between peak and trough drug levels." (148) Moreover, the psychoactive effect of THC can occur within seconds if marijuana is inhaled or take one-to-four hours if it is ingested. (149) That effect, however, lasts for a relatively short period. "[E]ven a high dose of smoked THC typically causes acute impairment of driving skills for only 3-4 hours." (150)

        The pharmacokinetics (the movement of drugs through the body) and pharmacodynamics (the effect of drugs and their mechanism of action) of cannabis are also far more complicated than the same features of alcohol. Alcohol dissolves in water or lipids, allowing it to become widely distributed; alcohol moves freely and is distributed fairly evenly throughout the body; it equilibrates rapidly between blood and brain tissue; and it produces no active metabolites. Because the lungs metabolize alcohol, the concentration in a person's breath approximates the level present in his blood or brain with a good deal of accuracy. (151)

        By contrast, THC readily dissolves in adipose tissue, so the amount detected in blood is not...

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