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As mentioned previously, there is a lack of high-quality data for assessing the prevalence of drug-impaired driving, as well as the relationship between drug-impaired driving and motor vehicle crash injury and fatality risk. Such data are necessary for assessing the efficacy of drug-impaired driving countermeasures. In their report, Advancing Drugged Driving Data at the State Level: Synthesis of Barriers and Expert Panel Recommendations Arnold & Scopatz (2016) listed 12 recommendations to States to address barriers to collecting and maintaining drug-impaired driving data. These recommendations included training law enforcement officers in performing SFSTs, authorizing officers to collect and test biological samples for drugs and alcohol among all drivers suspected of DWI, developing national model specifications for testing biological specimens, and developing or improving State data collection and reporting systems.

A first step in understanding the scope of the problem of drug-impaired driving is understanding the prevalence of drug use among drivers. One method of obtaining this information is the systematic collection of oral fluid or blood samples through a roadside survey. If performed rigorously with adequate sampling methods, such surveys are representative of the driving population in a given region over a specified time period. However, roadside surveys are not designed to assess drug impairment directly. Impairment is based on a variety of factors including dosage, time since administration, consumption of other psychoactive substances, the person’s tolerance of the drug, the person’s physiology, etc. Roadside surveys are designed to measure the presence/absence of drugs rather than impairment. In addition, roadside surveys are not designed to measure drug crash involvement or crash risk. Roadside surveys are useful for monitoring the driving public’s drug use over time and can be used to evaluate the impacts of implementing countermeasures, under certain conditions (Thomas et al., 2022). In 2007 NHTSA assessed the prevalence of drivers testing positive for alcohol and other drugs with the potential to impair driving-related behaviors (Lacey et al., 2009). The roadside survey was repeated in 2013 and 2014 (Kelley-Baker et al., 2017) and the report documented an increase in the prevalence of drivers testing positive for cannabis from 8.7% to 12.7%. States have also successfully performed high-quality, representative roadside surveys, an example being Washington State (Ramirez et al., 2016). For more information regarding best practices for State roadside surveys for alcohol and drug prevalence, see Thomas et al. (2022).

Another important component of describing the problem of drug-impaired driving is documenting the prevalence of drug use among drivers involved in crashes, including fatal crashes. Until recently, the information captured by FARS regarding the presence of drugs among drivers involved in fatal crashes was extremely limited (Berning & Smither, 2014). In 2018 NHTSA made several changes to FARS to improve the quality of the toxicological data. One change now allows all positive drug test results and some ability to record negative results. Previously, FARS allowed entry of only three substances, regardless of the number of drugs present in the biological sample (National Center for Statistics and Analysis, 2019). Other limitations identified by Berning and Smither (2014) remain, including differences in State drug testing and reporting. For a recent, comprehensive overview of current limitations associated with the drug data collected in FARS, see NHTSA’s 2022 report, Drug Testing and Traffic Safety: What You Need to Know (Berning et al., 2022).

Another approach to improving the quality of drug-impaired driving data is the creation of a State or Federal sentinel surveillance system. According to the Centers for Disease Control and Prevention, public health surveillance is “the systematic, ongoing collection, management, analysis, and interpretation of data followed by the dissemination of these data to public health programs to stimulate public health action” (Thacker et al., 2012, p. 3). In general, sentinel surveillance systems track the frequency of health events in a specified cohort for the purpose of estimating trends in a larger population. While initially intended for tracking infectious disease outbreaks, sentinel surveillance programs have been successfully used for monitoring the incidence of injuries and violence (Chow & Leo, 2017). Due to the effectiveness of sentinel surveillance systems in other fields, experts in transportation have long recommended the creation of a program for establishing the prevalence of drug-impaired driving (or at the least the prevalence of drivers testing positive for drugs), through enhancing existing surveillance systems, and the development of new systems, often involving the linkage of motor vehicle crash and health information, which may contain toxicology results (Kelley-Baker et al., 2019).

At the State level, from 1992 to 2013 NHTSA sponsored 20 States to link crash records to EMS, emergency department, inpatient hospital, death certificate, or medical examiner data as part of the CODES. As many health data systems collect toxicological information, linked crash and health data provides a unique opportunity to better understand the prevalence of drivers testing positive for drugs after a motor vehicle collision, for both fatal and nonfatal events (NHTSA, 2010). One CODES State, Kentucky, was able to supplement the information reported in FARS for their State by linking to death certificate data, increasing the capture of opioid and antidepressant cases (Bunn et al., 2019). The cessation of Federal funding for the CODES program in 2013 resulted in a reduction in State data linkage activities; however, in recent years, other States have initiated linkage programs independent of CODES (National Center for Injury Prevention and Control, 2019). While data linkage holds promise for an enhanced understanding of driving under the influence of drugs, many health data sources have similar limitations to FARS, including missing and incomplete toxicological information.

Although more costly than leveraging existing data systems, creating a new sentinel surveillance system designed specifically for monitoring drug and alcohol impairment may overcome many of the limitations discussed in this chapter. NHTSA began data research on the prevalence of drug and alcohol among serious and fatal road users presenting at selected trauma centers and medical examiners’ offices (Thomas et al., 2020; Thomas et al., 2022b). Insights from this study may serve as the basis for a future drug-impaired driving countermeasure for the development of a sentinel surveillance system. Indeed, Kelley-Baker et al. (2019) recommended Level I trauma centers as strong candidates for inclusion in such a sentinel surveillance system.