7.2 Drug-Impaired-Driving Laws

Overall Effectiveness Concerns: To date there have been no evaluations of the effect of drug-impaired-driving laws on the prevalence of drug-impaired driving or crashes.

It is illegal to drive under the influence of drugs or controlled substances in all 50 States, Puerto Rico, and the District of Columbia (Boddie & O’Brien, 2018). However, there is a great deal of variability in how States approach this issue. In some States impairment-based statutes stipulate that prosecution must prove the driver was impaired (for example, by driving recklessly or erratically). Some States have per se laws in which it is illegal to operate motor vehicles if there are specific detectable levels of the prohibited drug in drivers’ systems. Other States make it illegal to drive if there is a positive drug test. This is equivalent to “zero tolerance.” Some of these laws exclude prescription drugs or marijuana (Compton, 2017).

Lacey et al. (2010) conducted interviews with LEOs, prosecutors, and other traffic safety professionals in States with per se laws. Most were supportive of such laws. Although they did not believe per se laws made enforcement easier, they reported these laws had positive effects on the prosecution and conviction of drug-impaired drivers. Moreover, discussions with officers and prosecutors in States without per se laws also revealed relatively high conviction rates, with few cases reaching trial.

NHTSA’s 2009 Report to Congress included a model drug-impaired-driving law (Compton et al., 2009). Because the relationship between blood levels of drugs and driving impairment has not been established for drugs other than alcohol, the model law does not include a per se provision. However, NHTSA recommends States include enhanced penalties for drivers who are under the influence of drugs (including alcohol). In addition, NHTSA recommends State statutes provide separate and distinct offenses and sanctions for alcohol- and drug-impaired-driving (Compton et al., 2009; Compton, 2017). NHTSA’s 2017 Report to Congress also recommended measures for improved data and records maintenance at the State level, including the distinction between alcohol-use, drug-use, or both in impaired driving cases, and the distinction between the types of drugs. See Compton (2017) for a detailed list of recommendations.

For a detailed discussion of issues related to drug-impaired-driving laws, see DuPont et al. (2012). The authors make recommendations including improvement of drug testing technology, enactment of laws requiring drug testing of all drivers in injury crashes, and addition of drug use to underage zero-tolerance laws. See also Reisfeld et al. (2012) for arguments in favor of per se laws for drug-impaired driving and a discussion of the challenges of establishing impaired drug thresholds equivalent to .08 g/dL BAC. Finally, see NHTSA (2007) for recommendations to improve the prosecution of drug-impaired-driving cases.

Use: Twelve States (Arizona, Delaware, Georgia, Illinois, Indiana, Iowa, Michigan, Minnesota, Pennsylvania, Rhode Island, Utah, and Wisconsin) forbid the presence of any prohibited drug or its metabolites while drivers are in control of vehicles (NCSL, 2017). Six States (Kentucky, Nevada, North Carolina, Ohio, Oklahoma, and Virginia) allow drivers to be charged with impaired driving if any amount of specified drugs are found in them. Drivers under 21 may not drive with any amount of specified drugs (NCSL, 2017). In 18 States it is illegal for drivers to have any presence of marijuana in body fluid samples, and this includes 5 States (Montana, Nevada, Ohio, Pennsylvania, and Washington) with specific per se limits for THC ranging from 1 to 5 ng (GHSA, 2018). As of March 2019 there were 34 States and the District of Columbia that legalized marijuana use for medical purposes, and 12 States permitted the use low THC products that had high cannabidiol (CBD) for medical use (NCSL, 2019). More information about the drug-impaired-driving laws in each State can be found in NCSL (2019), Boddie & O’Brien (2018), NHTSA (2018), Lacey et al. (2010), and Walsh (2009).

Effectiveness: Lacey et al. (2010) tried to determine whether drug per se laws increased drug-impaired-driving arrests and convictions. However, they were hampered by the fact that many States do not record drug-impaired offenses separately from alcohol-impaired offenses. To date there have been no evaluations of the effect of drug-impaired-driving laws on the prevalence of drug-impaired driving or crashes. The GHSA recommends zero-tolerance laws over per se laws for illegal drug-, marijuana-, or opioid-impaired driving (Hedlund, 2018). Zero tolerance laws may be easier for drivers to understand over per se laws because, unlike standards for alcohol drinks, there are no standard measures of drug doses that can be consumed to stay below the per se levels (Hedlund, 2018).

Costs: The costs of drug-impaired-driving laws will depend on the number of offenders detected and the penalties applied to them.

Time to implement: Drug-impaired-driving laws can be implemented as soon as appropriate legislation is enacted, although time will be needed to train LEOs, prosecutors, and judges about the new legislation and to inform the general public.

Other issues:

• Per se laws and prescription medications: Some States with per se laws for drug-impaired driving exclude prescription medications from the list of prohibited drugs. Others require drivers to provide valid prescriptions to avoid being charged or convicted for drug-impaired driving. Using a medication as prescribed, however, can still lead to impairments in driving ability. For that reason, it is important that warning labels include information about the risks of using medications while driving. Also, physicians and pharmacists should counsel patients about driving risks, as appropriate. See the Alcohol- and Drug-Impaired Driving chapter, Section 7.3 for more information about patient education regarding medications. See also Smith et al. (2018) and Voas et al. (2013) for a discussion of issues related to per se laws and prescription medications.
• Drug testing of fatally injured drivers: Driver drug use is not reported in many fatal crashes. Moreover, there is inconsistent testing of drugs by laboratories, threshold differences for determining a positive test result, and variation in how results are reported. To better understand and track the drug-impaired-driving problem in the United States, improved data and data collection on drug-impaired drivers are needed, see Berning and Smither (2014). Logan et al. (2013) describe minimum recommendations for toxicological investigation of fatal motor vehicle crashes.
• Public support: There is strong approval among the general public for laws that prohibit drug-impaired driving. A 2013 survey by the AAA Foundation for Traffic Safety found that 80% of drivers support per se laws for marijuana (AAAFTS, 2014).