The influence of stimulants on truck driver crash responsibility in fatal crashes
Introduction
In order to combat the detrimental effects of fatigue, some truck drivers use licit and illicit stimulants [1], [2], [3]. Research suggests stimulants might improve both cognitive performance and driving performance when used to combat fatigue [4], [5], [6]. Even though stimulants can enhance cognitive functions such as vigilance, attention, psychomotor functioning, memory, and visuospatial/visuomotor abilities [7], [8], [9], research suggests they create driving impairments [10], [11], [12]. Stimulants are frequently detected in tests on truck drivers killed in work-related crashes [13], [14] and in deceased drivers deemed to be at fault in such crashes [15], [16].
Estimates of stimulant use among commercial truck drivers involved in crashes vary. In studies of fatally injured truck drivers, Australian research reported prevalence estimates between 9.83% and 23% [13], [14], [16]. Crouch et al. [15] found that 22% of their United States sample (37 out of 168 truck drivers) tested positive for stimulants. In studies of non-fatally injured drivers, prevalence estimates vary further. For example, Longo et al. [17] found that only 1.8% of their Australian sample tested positive (one out of 55 truck drivers). In self-report studies prevalence estimates are even higher at 27.5% [3] and 91.4% [2].
Although stimulant use was detected among many drivers involved in crashes this does not imply a causal relationship. Research on culpability among stimulant-positive truck drivers is limited; at the time of the present study, only one such study was found. In 2004 Drummer et al. found stimulants present in 15.8% (22 out of 139) of a sample of deceased truck drivers who were deemed at fault in the crash, resulting in an OR of 8.83 (95% CI: 1.00–77.8) [16]. Some limitations for this study are evident. For example, the analysis was underpowered given the small number of truckers positive for stimulants and negative for other drugs and alcohol. The lack of power results in a wide confidence interval. Further, the lower confidence interval limit being equal to one indicated marginal statistical significance. Also, driving-related risk taking behavior and/or poor driving abilities were not controlled for (nor could they be given the lack of power available). Specifically, drivers who had taken stimulants might be at an increased risk for crash responsibility due to a general tendency to take risks while driving or simply because they are poor drivers. Finally, all drivers in this study were killed as a result of the crash, and results may differ in non-fatally injured drivers.
Despite links with crashes, stimulants may improve driving-related cognitive functions (e.g., attention, psychomotor functioning, memory, visuospatial and visuomotor abilities) [7], [8], [9], [18], [19]. Research also indicates that stimulants cause improvements in vigilance performance [7], [19]. Vigilance tasks (also known as monitoring tasks) require one to sustain attention while attempting to identify randomly occurring unusual events on a computer monitor. In addition to improving performance under normal vigilance conditions, stimulant use can return vigilance performance to baseline in fatigued participants, even after lengthy periods of wakefulness (e.g., 22–85 h without sleep) [20], [21], [22]. However, some studies using driving simulators suggest driving deficits such as swerving, speeding, erratic driving, and risk taking with stimulant use [10], [11], [12].
Little research exists on the prevalence of stimulant use among North American transport truck drivers. Research on crash responsibility is also scarce. One goal of our study was to report the percentage of truck drivers testing positive for stimulants both overall (from 1993 through 2008) and year-by-year. The principal goal of this study was to assess whether stimulant use increases the odds of performing unsafe driving actions (UDAs: a proxy measure for crash responsibility) while improving on previous research by using a large sample, controlling for confounding variables, and including drivers regardless of whether they were fatally injured in the crash. We hypothesized that stimulant-positive drivers would be at increased odds of committing any UDA compared to stimulant-negative drivers. Finally, we examined crash responsibility by stimulant exposure for the most reported unsafe driving actions.
Section snippets
Data source
All analyses for the present study were calculated using the Fatality Analysis Reporting System (FARS) database. Since 1975 the National Center for Statistics and Analysis of the National Highway Traffic Safety Administration in the United States has compiled information on fatal traffic crashes for 50 states, Puerto Rico, and the District of Columbia. For inclusion in the FARS database the crash must have occurred on a trafficway that is normally open to the public and the crash must have
Prevalence of drugs and driving infractions
Between 1993 and 2008 there were 75,098 records for truck-tractors or trucks with a GVWR greater than 26,000 lbs. Of these, 65,867 were truck driver records, 9159 were truck passenger records, and 72 had passenger type missing. Of the 65,867 truck driver records, 174 drivers were below the age of 20 and 332 drivers had no age recorded. These were excluded, leaving 65,361 truck drivers for the prevalence analysis (99%) of which 10,190 (15.5%) were tested for drugs. For all truck drivers, we found
Discussion
Of the 65,361 truck drivers involved in fatal crashes, 10,190 were tested for drugs, of which 372 tested stimulant-positive. Depending on the denominator chosen annual detection rates ranged between 0.27% and 0.98% for all truck drivers and 2.15% and 6.26% for truck drivers tested for drug use (see Fig. 1). The true prevalence rate likely lies between these two extremes. It should be noted that the FARS database aggregates state-level data and therefore drugs tested may differ by jurisdiction.
Conclusions
Overall, the results of this study demonstrate that few transport truck drivers were under the influence of stimulants but those who were had increased odds of committing an unsafe driving action, a proxy measure of crash responsibility, compared to truck drivers not under their influence. The results of the present study provide four suggested improvements for future culpability studies. The first improvement addresses potentially inflated prevalence estimates. Given that deceased populations
Acknowledgements
The authors acknowledge financial support from AUTO21-Network of Centers of Excellence and the Ontario Neurotrauma Foundation. Michel Bédard is a member of CanDRIVE (a New Emerging Team funded by the Canadian Institutes of Health Research, Institute of Aging) and is a Canada Research Chair in Aging and Health (www.chairs.gc.ca); he acknowledges the support of both programs.
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