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7 TABLE 1 NIDA'S DRUG CLASSIFICATION Drug Category Examples of Drugs in Category 1. Cannabinoids marijuana, hashish 2. CNS Depressants barbiturates, benzodiazepines, flunitrazepam, GHB, methaqualone 3. Dissociative Anesthetics ketamine, PCP, and analogs 4. Hallucinogens LSD, mescaline, psilocybin 5. Opioids and Morphine codeine, fentanyl and analogs, heroin, morphine, opium, oxycodone HCL, Derivatives hydrocodone bitartrate, acetaminophen 6. CNS Stimulants amphetamines, methamphetamines, cocaine, MDMA, methylphenidate, nicotine (add in caffeine and ephedrine here even though they are not illegal) 7. Other Compounds anabolic steroids, dextromethorphan, inhalants Source: NIDA (2006). PCP = Phencyclidine; HCL = hydrogen chloride; MDMA = 3,4-Methylenedioxymethamphetamine (ecstasy). disease entity rather than on the medications themselves. aspects of reasoning, judgment, decision making, reaction The exceptions are insulin, 391.41(b)(3), which is forbidden time, remaining continuously alert, paying attention to details, for use by drivers of commercial vehicles (except by wavier using keen visual perception during vigilance (visual, auditory, under 49 CFR 391.64) and controlled substances, which are and kinesthetic vigilance), monitoring information, navi- forbidden with the notable exception under 391.41(b)(12). gating between locations, responding to hazards on the road, Insulin will not be discussed in detail here. and so on. Because this synthesis is primarily designed to serve the In the case of commercial drivers, other cognitive aspects roadway safety community, the chemical substances described of the job entail communication interactions with employers, here could be categorized into clusters of the "most likely dispatchers, shippers, and receivers. Bus and motorcoach substances to be ingested by commercial drivers" and into drivers interact with passengers, charter and tour coordinators, additional categories that address "how these chemicals are tour-guide personnel, and others. In addition to the obvious likely to impact vehicle driver performance, safety, and health"; physiological and cognitive tasks mentioned previously, that is, as (1) hypnotics and sleep-promoting compounds; many truck drivers carry out numerous physical activities and (2) stimulants and alertness-producing compounds; and other ancillary duties involving pre-trip safety inspections, (3) hormonal, herbal, dietary, and energy-boosting supple- loading and unloading of cargo, securing loads (tarping, ments. This latter scheme of chemical categorization is largely chaining, etc.), applying heavy chains to wheels, fueling, and followed in this synthesis report. However, combinations of other aspects of the job; whereas bus and motorcoach drivers, these categorizations are evident in the narrative descriptions especially those involved in driving tour groups, often handle presented, as some chemical substances belong to more than significant amounts of baggage (Krueger and Van Hemel 2001). one of the several categories that fit their description. Therefore, simply stating that a chemical substance or a drug affects performance readily invokes a question of what is CHEMICAL SUBSTANCE EFFECTS implied by "performance" and how much of a drug effect is AND DRIVING PERFORMANCE unacceptable for accomplishing individual tasks, completing a job, violating some safety principle, and risking adverse The second issue of importance for this synthesis is to driving incidents. present research findings about chemicals such that the results cited relate to commercial driver performance and In June 2005, TRB's Committee on Alcohol, Other Drugs health. Relating many of the published drug performance and Transportation held a symposium to discuss the role of effects from laboratory studies to the performance of com- Drugs in Traffic. Many of the experts addressed involvement mercial drivers in on-the-road scenarios can be tenuous. of drugs (licit and illicit) in traffic injuries and deaths. In his Driving any ground vehicle involves many task elements, presentation on Drug Effects and their Significance for Traffic including physically handling the machinery (a car, bus, truck, Safety, Shinar (2005) suggested that several implicit assump- or motorcycle) by steering, shifting gears, braking, staying tions are usually made in the study of drugs and their effects within the lanes on the road (lane tracking), manipulating a on performance: vehicle through physical obstacles (e.g., highway, country, and city driving, in traffic, backing-up, and parking). The act Psychoactive drugs should have an effect not only on mood but of driving also involves many psychological and cognitive also on cognitive and psychomotor functioning. Furthermore,

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8 these effects should be reflected in performance on measures able stages associated with drivers' perception-response time related to these functions (such as stability, reaction time, and immediately before becoming involved in a crash sequence, speech) and should reflect some significant deviation from the norm. including detection, identification, decision, and response, These cognitive changes are expected to be of such magnitude demonstrating that in-depth assessments of driver reaction that they are both observable to a trained person and quantifiable time (e.g., in accident reconstruction) are not a trivial matter with some standardized tests. Since driving is a fairly complex psychomotor and cognitive (Olson 2007). task, drug impairments should affect driving performance, usually in a negative manner. Not only is driving a fairly complex psychomotor and Individuals who take drugs often drive while under their influ- cognitive task, but it is a planned behavior. Different persons ence, either because they do not appreciate their impairments or because their judgment is impaired. may drive from the same starting point to the same end point The resulting Driving Under the Influence of Drugs (DUI) while employing different strategies; from the level of trip problem can be dealt with in much the same way as DWI planning, to navigation, to reacting to specific situations. The (Driving While Intoxicated--with ethanol) (Shinar 2005, p. 68). additional involvement of chemical substances in driving scenarios make cause-and-effect analyses even more difficult, The focus of this synthesis report is not on the role of drugs and can obfuscate even the simplest explanations of drug- in crashes, but rather on what is known about the effects induced response times reported in the experimental literature. of chemicals on driving performance per se. This synthesis For example, individuals under the effects of alcohol often reviews, in brief, numerous scientific and research-oriented experience overconfidence in their driving, and they speed. studies in the literature. For scientists and researchers defining In contrast, individuals under the effects of marijuana often theoretical and empirical questions to be answered through feel impaired and tend to drive slower. However, both drugs good basic laboratory and applied field experiments is key to impair judgment and the ability to respond correctly to emer- determining the impact of chemical substances on sleep and gency situations (Shinar 2005, 2007b). alertness (loss or gain) and on work-related performance (enhancement or degradation). The most important factors There is also the issue of individual differences in the vari- are the "measures of performance" that provide the best under- ability of metabolism and behavioral responses or reaction standing of the effects of various drugs or other chemical effects to medications, drugs, and other chemicals. Metabolism substances as they are related to driver performance on the and effects of drugs on individuals vary, in some cases quite roadway. It is not sufficient to report that an experimental significantly. That is, some people appear to manage satisfacto- study found that a single ingestion of a particular dose of a rily with medications or chemical substances that in a similar drug affects certain lab-based task performances that appear situation would severely impair another person's behavioral to be of little practical consequence, or in particular to report responses (McBay 1997; Shinar 2007b). degradation in performance types that do not appear to have direct application to driving a truck or bus or motorcoach. These considerations raise important questions of how For example, stating that a particular drug "alters a person's best to relate laboratory-based psychological and physiolog- critical flicker fusion: CFF," or it "adversely affects psycho- ical performance measures to predicting driver behavior in motor tracking, or reaction time, or judgment, or decision- "real world" situations on the highway. Obtaining and inter- making," without offering practical examples of how to apply preting research quality measures of driving performance is the finding to vehicle driving circumstances necessitates not simple. From these descriptions it can be understood that a "stretch of inference" for understanding the implications determining that drugs in a laboratory experiment affect regarding roadway safety. cognitive performance on generic psychological tasks is not always readily transferable to real-world roadway experiences. One such set of scientific issues was delineated by Babkoff For example, some experiments have demonstrated that and Krueger (1992) who identified a set of at least eight whereas low doses of a drug given to an experimental partic- plausible research protocol criteria (mostly based on measures ipant produce slight performance effects, these slight effects of reaction time and measures of performance accuracy) that can actually become more pronounced when the nature of the could be examined in laboratory experiments for deciding task asked of research subjects is intensified, such as when the whether or not to use a stimulant to ameliorate performance cognitive workload is increased or when subjects are asked degradation effects attributable to excessive sleep loss. This to do multi-tasking (Pickworth et al. 1997; Shinar 2007). The they identified in a paradigm with a particular aim of sustain- "application leap" from lab-based findings to the "real world" ing soldier performance during near continuous, around-the- is often not an easy one. Researchers usually agree however clock military operations, where typically not much sleep is that if a drug adversely affects a fine-tuned measure of human obtained by operational personnel. However, even reaction performance (e.g., reaction time, signal detection, or precision time measures are not always straightforward indications of tracking) in a controlled laboratory study it is reasonable to equipment operator performance. Human factors research expect that such a drug-affected performance is not likely to specialists involved in roadway crash investigations point improve while the individual is driving; performance on the to the many nuances and fine points of at least four identifi- road might even be worse.