Welcome to Issue #17
Welcome to Directions: The Newsletter of the Judicial Resource Center on Drug-Impaired Driving. Each month we’ll bring the latest case law, judicial resources, articles, and more right to your email inbox. For previous issues or to subscribe, please click here. Additionally, we invite you to check out our Resource Center, a repository of educational materials on drug-impaired driving, hand-selected for the judiciary. If you have materials you want considered for inclusion in either our newsletter or resource center, please contact us at: trafficresources@judges.org
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Cannabis & impaired driving: What the research tells us
by Hannah Barrett & Robyn Robertson
Traffic Injury Research Foundation
In recent years, an increasing number of jurisdictions have adopted legislation permitting the consumption of recreational or medical cannabis products. As of July 2022, 19 US states have legalized recreational cannabis, with many more permitting the use of medical cannabis products. With this continuing trend, concern about cannabis-impaired driving has grown, and this issue has important implications for drug-impaired driving prevention strategies
Work is needed to develop effective road safety policies distinguishing between cannabis-impaired driving and the prior use of cannabis only. In addition, education about the effects of cannabis and ways it impairs driving skills is essential to inform decision-making among criminal justice practitioners handling impaired driving cases. This article summarizes the most current research on cannabis impairment and driving risk based on laboratory and real-world studies and describes how cannabis affects crash risk as well as tools to identify impairment. Knowledge about the effects of medical cannabis on driving is also shared.
How does cannabis impair driving skills?
Driving is a divided attention task involving the combined use of cognitive, visual/auditory and motor skills. One of the most common measures to assess impairment of driving skills in research studies is the standard deviation of lateral position (SDLP), which is a measure of weaving, swerving, and overcorrecting within a lane. SDLP is sensitive to the effects of alcohol and drugs, and studies assess the impact of impairment on these functions using driving simulators. Other driving measures to gauge impairment include reaction time, headway between vehicles, weaving outside a lane, and driving speed. While several studies have confirmed cannabis impairs driving as measured by SDLP, the degree of impairment produced varies according to several factors including THC dose, the characteristics of the person consuming it, and the method of ingestion. Of importance, while research shows cannabis does produce driving impairment at a population level, it may not always produce impairment at an individual level. This is due to several factors mentioned above.
There is also a notable distinction between occasional and chronic frequent cannabis consumers and how THC impairs their driving skills. One study showed only occasional consumers were substantially impaired, whereas among chronic frequent consumers neither 10 nor 20 mg THC produced clinically relevant driving impairment (Bosker et al., 2012). While this does not mean THC is harmless for chronic frequent consumers, it indicates frequent consumers do develop some degree of tolerance to the impairing effects. At the same time, some of them may consume higher doses of THC to overcome their tolerance and achieve a high, which may still impair their driving. Moreover, while there is some evidence that persons taking cannabis are more aware of their impairment and therefore may be more reluctant to drive initially, other studies have suggested drivers consuming cannabis also may subjectively feel okay to drive even when their driving skills remain impaired. Notably, studies have also shown cannabis impairment increases headway, meaning drivers leave a larger gap between them and the vehicle ahead, as a compensatory mechanism they use when they think they are driving impaired (Hartman & Huestis, 2013; Lenne et al., 2010; Robbe, 1998).
How does cannabis affect crash risk?
When consumed alone, cannabis is associated with a modest increase in crash risk at the population level when compared to the absence of cannabis. While the increase in crash risk varies, the average increase is 30% to 40% meaning drivers who test positive for cannabis are approximately 1.3 to 1.4 times more likely to be involved in a crash than drivers without cannabis (Rogeberg, Elvik, & White, 2019). In other words, the crash risk associated with cannabis is lower than for alcohol, but there is still some risk.
How does cannabis affect crash risk?
Are all drivers who consume cannabis-impaired?
No, at the population level, the higher the THC concentration in blood, the greater the proportion of cannabis consumers who show impairment. This is clearest among occasional cannabis consumers, but it differs among frequent consumers who develop a partial tolerance to THC effects. However, at the individual level, it is difficult to predict impairment in specific drivers. A dissociation between blood THC concentrations and their impact on psychomotor function and cognition exists for several reasons. For example, after chronic daily cannabis intake, THC (above 1 ng/mL) can be detected in the blood for many days, including in the absence of impairment. Further, in road traffic incidents, THC concentrations are typically detected in blood up to one to eight hours after a traffic crash or stop. This does not represent THC concentration at the time of the crash, as blood THC concentrations decrease by approximately 74% in the first 30 minutes and by 90% in the first 1.4 hours.
Does medical cannabis produce impairment in drivers?
Medical cannabis alone, when consumed under the supervision of a medical professional to overcome conditions that may impair driving such as physical pain, is less likely to produce impairment. However, most medical cannabis products include cannabidiol (CBD) or THC as a primary ingredient, and many products include some concentration of THC. Cannabidiol alone generally does not impair driving, and medical products are less likely to produce driving impairment when taken as directed by physicians. People consuming medical cannabis typically take it more frequently than recreational consumers, resulting in the development of pharmacological and behavioral tolerance to the effects of THC. Furthermore, medical consumers may be more likely than recreational consumers to use cannabis products with lower THC content, potentially reducing their collision risk.
What tools are available to detect cannabis-impaired drivers?
Law enforcement and road safety agencies would like to rely on a per se limit for THC in impaired driving legislation, analogous to a blood alcohol concentration (BAC) limit for alcohol. However, research shows it is exceedingly difficult to accurately identify a THC limit at which most drivers are impaired because of how the drug is metabolized in the body. As such, it is important to understand what other detection tools can identify cannabis-impaired drivers.
SFSTs. Standardized field sobriety tests (i.e., horizontal gaze nystagmus, one-leg stand and walk and turn) were developed to identify alcohol impairment. Currently, they have not been validated for cannabis and do not, as a whole, adequately detect THC-induced driver impairment, although some individual tests show promise. The major barrier is distinguishing THC-related impairment from driving performance when not drug-affected. Such reference data can be collected in laboratory settings but cannot be collected at the roadside. Without this data, standards of cannabis impairment are difficult to define for behavioral tests performed on drivers at the roadside.
Oral fluid. Oral fluid test results indicate the concentration of cannabis present in a sample but are difficult to link to blood results or driver performance. Positive oral fluid test results may indicate recent cannabis use because test sensitivity is usually limited to a few hours after smoking (the time depends upon the detection threshold of the device) (Swortwood et al., 2017). Two to four hours after cannabis intake, the coating of the oral fluid dissipates, and oral fluid THC concentrations approximately parallel blood THC concentrations, but not at the same levels (Desrosiers & Huestis, 2019). Blood THC concentrations cannot be accurately estimated from oral fluid concentrations because of high intra-subject and inter-subject variability (Busardo et al., 2018).
Conclusions
The science of cannabis impairment is complex with important nuances to the conclusions which can be drawn. The adjudication of cannabis-impaired driving cases requires a clear understanding of how cannabis is metabolized and effects the body as well as driving skills. Important case considerations include clearly articulated evidence of driving behavior, results of behavioral and biological tests, as well as an understanding of the frequency of the driver’s past and present cannabis use. More information about these topics was compiled by the Drugged Driving Work Group of the International Conference on Alcohol, Drugs & Traffic Safety comprised of 24 leading researchers from 11 countries who summarized the science in a fact sheet series available at: https://druggeddriving.tirf.ca/resources/
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References
Arkell, T. R., Vinckenbosch, F., Kevin, R. C., Theunissen, E. L., McGregor, I. S., & Ramaekers, J. G. (2020). Effect of cannabidiol and Δ9-tetrahydrocannabinol on driving performance: a randomized clinical trial. JAMA, 324(21), 2177-2186.
Banta-Green, C., Rowhani-Rahbar, A., Ebel, B. E., Andris, L. M., & Qiu, Q. (2016). Cannabis use among drivers suspected of driving under the influence or involved in collisions: Analyses of Washington state patrol data.
Bosker, W. M., Kuypers, K. P., Theunissen, E. L., Surinx, A., Blankespoor, R. J., Skopp, G., ... & Ramaekers, J. G. (2012). Medicinal Δ9 tetrahydrocannabinol (dronabinol) impairs on the road driving performance of occasional and heavy cannabis users but is not detected in Standard Field Sobriety Tests. Addiction, 107(10), 1837-1844.
Brubacher JR, Chan H, Erdelyi S, Macdonald S, Asbridge M, Mann RE, et al. Cannabis use as a risk factor for causing motor vehicle crashes: a prospective study. Addiction. 2019; 114(9):1616-26.
Busardo, F. P, Pichini, S., Pellegrini, M., Montana, A., Fabrizio Lo Faro, A., Zaami, S., & Graziano, S. (2018). Correlation between blood and oral fluid psychoactive drug concentrations and cognitive impairment in driving under the influence of drugs. Current Neuropharmacology, 16(1), 84-96.
Desrosiers, N. A., & Huestis, M. A. (2019). Oral fluid drug testing: analytical approaches, issues and interpretation of results. Journal of Analytical Toxicology, 43(6), 415-443.
Downey, L. A., King, R., Papafotiou, K., Swann, P., Ogden, E., Boorman, M., & Stough, C. (2012). Detecting impairment associated with cannabis with and without alcohol on the Standardized Field Sobriety Tests. Psychopharmacology, 224(4), 581-589.
Elliott, S. P., Stephen, D. W., & Paterson, S. (2018). The United Kingdom and Ireland association of forensic toxicologists forensic toxicology laboratory guidelines (2018). Science & Justice, 58(5), 335-345.
Hartman, R. L., & Huestis, M. A. (2013). Cannabis effects on driving skills. Clinical Chemistry, 59(3), 478-492.
Lenné, M. G., Dietze, P. M., Triggs, T. J., Walmsley, S., Murphy, B., & Redman, J. R. (2010). The effects of cannabis and alcohol on simulated arterial driving: influences of driving experience and task demand. Accident Analysis & Prevention, 42(3), 859-866.
Marcotte, T. D., Umlauf, A., Grelotti, D. J., Sones, E. G., Sobolesky, P. M., Smith, B. E., ... & Fitzgerald, R. L. (2022). Driving performance and cannabis users’ perception of safety: A randomized clinical trial. JAMA Psychiatry, 79(3), 201-209.
Peck, R. C., Gebers, M. A., Voas, R. B. & Romano, E. (2018). The relationship between blood alcohol concentration (BAC), age, and crash risk. J Safety Res 39, 311-319, doi:10.1016/j.jsr.2008.02.030
Ramaekers, J. G., Robbe, H. W. J., & O’Hanlon, J. (2000). Marijuana, alcohol and actual driving performance. Human Psychopharmacology: Clinical and Experimental, 15(7), 551-558.
Robbe, H. (1998). Marijuana’s impairing effects on driving are moderate when taken alone but severe when combined with alcohol. Human psychopharmacology: Clinical and Experimental, 13(S2), S70-S78.
Rogeberg O, Elvik R, White M. Correction to: ‘The effects of cannabis intoxication on motor vehicle collision revisited and revised’ (2016). Addiction. 2018;113(5):967-9.
Swortwood, M. J., Newmeyer, M. N., Andersson, M., Abulseoud, O. A., Scheidweiler, K. B., & Huestis, M. A. (2017). Cannabinoid disposition in oral fluid after controlled smoked, vaporized, and oral cannabis administration. Drug Testing and Analysis, 9(6), 905-915.
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Recent Cases of Note
by Earl G. Penrod, Senior Judge
Indiana Judicial Outreach Liaison
Judge in Residence, National Judicial College
Reasonable Suspicion based on informant/tipster (driver’s fourteen-year-old daughter)
Police conducted an investigatory stop for impaired driving based on a 9-1-1 call that reported a possible drunk driver at the Dollar Tree store. The 14-year-old caller identified herself and stated that her mother was driving a white van at the Dollar Tree and sounded drunk. After observing a female get into the white van and drive away, the police stopped the vehicle even though they did not observe any erratic behavior or traffic violations. Resulting from the stop, the driver was arrested and charged with DWI. The trial court denied Defendant’s Motion to Suppress and the South Dakota Supreme Court in a de novo review reached the same conclusion that the stop was lawful.
The South Dakota Supreme Court notes that reasonable suspicion supporting an investigatory stop is “a common-sense, non-technical concept dealing with practical considerations of everyday life.” Investigatory stops may be based on information provided by informants (tipsters) and if criminal activity is observed by an informant whose identity is known, law enforcement corroboration of the alleged criminal activity may not be necessary. Further, when the informant accurately predicts future behavior, the informant is demonstrating a special familiarity with a person’s affairs and such inside information supports a reasonable belief that the tipster has reliable information about the person’s illegal activities. The Court found that the totality of the circumstances including the 14-year-old daughter’s report that her mother sounded drunk, was getting ready to leave the Dollar Tree parking lot and had a history of leaving the daughter in a vehicle and disappearing and drinking supported a finding of reasonable suspicion for the investigatory stop.
The dissent indicated that there was NOT reasonable suspicion to make the investigatory stop because the daughter’s report was a conclusory allegation of intoxication and there was no corroborating evidence such as whether the daughter had ever observed her mother intoxicated or had any training or experience in identifying signs of intoxication. Further, the officers could have failed to check the motivation and basis for the daughter’s report. State v. Rosa, 2022 SD 76 (2022 S.D. LEXIS 143)
Cell Phones at Scene of Crash, Search Warrants, Good Faith Exception to Exclusionary Rule
A warrant was issued to search three cell phones found at the scene of a fatal crash. A blood test conducted pursuant to a separate warrant showed amphetamine, methamphetamine, and fentanyl in the system of the driver who had driven left of the center, killing another driver. The affidavit supporting the warrant to search the three phones indicated that the phones may contain evidence regarding the active aggravated-vehicular homicide investigation. While searching the phone, police discovered pictures of nude juveniles and the defendant was subsequently charged with pandering obscenity involving a minor as well as felony aggravated vehicular homicide. The trial court denied the defendant’s Motion to Suppress, and the Court of Appeals found that there was insufficient probable cause for the search warrant for the phones as the State failed to show a connection between the phones and the crash. However, the Court of Appeals upheld the cell phone search based on the good faith exception to the Exclusionary Rule as set forth by the United States Supreme Court in U.S. v. Leon, 468 U.S. 897 (1984). The Ohio Supreme Court reversed and remanded finding that the good faith exception was not applicable in this case.
The Supreme Court majority provides a review of the Exclusionary Rule and the good-faith exception found in Leon, supra, that permits a police officer to rely on a search warrant issued by a judicial officer when the police act in an objectively reasonable manner, even if the warrant is later found defective. The Court noted that in some circumstances, it would NOT be objectively reasonable for an officer to rely on a warrant such as when the supporting affidavit, is so lacking in indicia of probable cause to render the official belief of probable cause unreasonable. That is, a bare-bones affidavit fails to establish a minimally sufficient nexus between the item to be searched and the underlying criminal activity and even though a judicial officer had found probable cause, police have a duty to act reasonably in protecting an individual’s Fourth Amendment rights by not executing a warrant that is so lacking in probable cause that no well-trained officer would reasonably rely on it.
Three Justices dissented and would have upheld the application of the good faith exception. The dissent claimed that the majority had conflated a bare-bones affidavit and an affidavit lacking probable cause. In summary, even though the affidavit did not provide probable cause for the issuance of a warrant, there was sufficient connection between the automobile crash and the cell phones so that it was not bare bones, and it was reasonable for the police to rely on it in conducting the search.
State v. Schubert, 2022-Ohio-4604, 2022 Ohio LEXIS 2599 (December 22, 2022)
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