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American Journal of Epidemiology Advance Access originally published online on August 22, 2007
American Journal of Epidemiology 2007 166(11):1320-1326; doi:10.1093/aje/kwm205
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American Journal of Epidemiology © The Author 2007. Published by the Johns Hopkins Bloomberg School of Public Health. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org.

ORIGINAL CONTRIBUTIONS

Predictors of Psychostimulant Use by Long-Distance Truck Drivers

Ann Williamson

From the New South Wales Injury Risk Management Research Centre, University of New South Wales, Sydney, NSW, Australia

Correspondence to Dr. Ann Williamson, NSW Injury Risk Management Research Centre, University of New South Wales, Building G2, Western Campus, UNSW Sydney, NSW, Australia, 2052 (e-mail: a.williamson{at}unsw.edu.au).

Received for publication March 19, 2007. Accepted for publication June 8, 2007.


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
Two national cross-sectional surveys of fatigue and its effects in long-distance road transport in Australia showed that stimulant use was a common feature of this industry. Between one in five and one in three drivers reported using stimulants at least sometimes, and a significant proportion reported stimulant use as a most helpful fatigue management strategy. This study reanalyzed the surveys with the aim of identifying predictors of stimulant drug use by drivers. The surveys were administered in 1991 (n = 970) and 1998 (n = 1,007) by interview and self-administration. Logistic regression analysis conducted separately for each survey showed that stimulant drug use was twice as likely for drivers who had the greatest problem in managing fatigue and was two to three times more likely for drivers paid on a payment-by-results or contingency-payment basis. Younger, less experienced drivers were also more likely to take drugs. This analysis demonstrates the involvement of external factors, especially productivity-based payment systems, in stimulant drug use by truck drivers; findings were confirmed in two separate surveys conducted 7 years apart. Results highlight the important role of economic and organizational factors in occupational health and safety problems.

central nervous system stimulants; fatigue; motor vehicles; salaries and fringe benefits; substance-related disorders


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
In studies in the United States, Australia, and the Netherlands (1, 2), psychostimulant use has been implicated as increasing the risk of fatal and injury crashes, especially for occupational driving, such as long-distance trucking (2, 3). In fatal crashes in Australia, stimulants were found five times more often in truck drivers than in all drivers (3), and surveys of long-distance truck drivers showed that 20–30 percent of drivers reported using stimulants, mainly illegally obtained forms of amphetamines, while driving (4–6).

The importance of stimulant use in this industry is highlighted by findings that long-haul truck drivers who use stimulants rate them as one of the most effective strategies for managing fatigue (5, 6). Although stimulants can make drivers feel less sleepy and, at low doses, can benefit driving performance through improved reaction speed, attention, and concentration (7), other research demonstrates driving impairments such as risky behavior (8), increased sleepiness due to withdrawal from stimulants, and the overall effects of high doses (9). Evidence from crash studies also shows that drivers using stimulants are more likely to be the culpable driver (2).

Unfortunately, reducing the use of stimulants in the long-distance road transport industry is not a simple matter. Making stimulant use while driving illegal is clearly not a sufficient strategy to deter a notable minority of drivers. Attempts to reduce stimulant use in the long-distance road transport industry need to focus on the reasons that drivers use stimulants and find them helpful for managing fatigue. This was the aim of this study: to identify the predictors of stimulant drug use by long-distance truck drivers.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 References
 
The results of two surveys of the long-distance road transport industry were analyzed, with particular emphasis on questions regarding the use of psychostimulant drugs to stay awake while driving. The first survey was conducted in 1991 and was distributed to drivers in all states of Australia except Tasmania. The second survey was conducted in 1998 and included drivers from all states except Western Australia and Tasmania. The characteristics of each of the surveys are described below.

Survey 1
Participants.
A total of 970 drivers participated in this survey. Almost all were male (n = 950). Approximately two thirds (68.5 percent) completed an anonymous, self-administered form, and the remainder of the drivers were interviewed.

Materials.
The survey included the following:

  1. Driver and vehicle information, including demographic details about the driver and details about the driver's employment (owner or employee driver, company size, heavy-vehicle driving experience, and type of payment received)
  2. Fatigue, including information about the driver's experience with and attitudes toward fatigue and to potential fatigue countermeasures
  3. Details of the last trip, including amount of work and rest time, sleep patterns, and when fatigue was experienced
  4. Details of work/rest schedule in the last week, including duration of work
  5. Details of remuneration, including type and amount of payment
  6. Reports of breaking the road rules and working-hours rules and the reasons for rule breaking

The specific item relating to stimulant use was, "Please indicate how often you use the strategies listed below in an attempt to deal with your driver fatigue during trips." Sixteen options were provided, including "taking stimulant drugs," and drivers were asked to respond to the options—often, sometimes, rarely, or never—and then to indicate which of the 16 strategies they found most helpful.

Procedure.
The survey was administered in two forms: a self-administered form (4,086 distributed) and a structured interview (371 invitations). Long-distance drivers, completing trips of at least 300 km, were invited to participate. Because no details were available about the number of drivers or trucks in the industry, a broad sampling strategy was adopted. The self-administered form was distributed directly to drivers at major truck stops or terminals (15.9 percent of self-administered surveys) or to drivers through trucking companies (83.4 percent of self-administered surveys). A postage-paid envelope was attached to each survey so drivers could return the completed survey directly to the survey team. Interviews were conducted at truck stops or terminals and at one company. Drivers agreeing to participate were told the purpose of the survey and that it was anonymous, and they were either interviewed on the spot or handed a survey and reply-paid envelope to return the survey when it was completed. Distribution of surveys through companies involved contacting management to explain the study purpose and methods, then providing surveys to those who agreed to participate. Further details of recruitment are provided elsewhere (5).

The response rate for self-administered surveys distributed at truck stops was 18.7 percent and at companies was 15.6 percent. For interviews, the participation rate was high at 81.4 percent of drivers. To check for potential selection bias due to low response rate for self-administered surveys, interview and self-administered survey results were compared. No significant differences were found (5).

Survey 2
Participants.
In total, 1,007 drivers participated in the survey, with 48.2 percent completing a self-administered survey form and the remainder completing an interview.

Materials.
The survey content was the same as for the first survey except that the Epworth Sleepiness Scale—a standard measure of chronic sleepiness (10)—was added, two additional questions on reported experience with fatigue-related dangers were included, and questions on expected time of arrival were removed. Questions relating to psychostimulant use were the same as those for the first survey.

Procedure.
Full details of recruitment are provided elsewhere (6). Regarding the self-administered questionnaire, 1,449 questionnaires were handed out; for the interviews, 565 drivers were invited to participate. Long-distance drivers, completing trips of at least 300 km, were recruited at truck stops. Drivers were invited to participate in interview or self-administered versions of the questionnaire. Overall, 485 self-administered questionnaires were returned, a response rate of 34 percent, and 522 interviews were conducted, a 92 percent response rate. Potential selection bias due to low response rates for self-administered surveys was checked by comparing results of the two distribution methods. No significant differences were found between the self-administered and interview methods (6).

Data analysis
The results of each survey were grouped according to drivers' self-reported frequency of stimulant use (often, sometimes, rarely, never). Each survey was analyzed independently because doing so provides an opportunity for confirmatory analysis. Bivariate analysis using chi-square or analysis of variance (two-sided tests) was conducted on frequency of drug use by variables relating to personal and work characteristics, fatigue experiences and attitudes, and infringements of self-reported road rule and working-hours regulations. Multivariate analysis was performed by logistic regression separately for each survey. A binary dependent variable of drug use was created, with drivers who reported using drugs at all while driving (often, sometimes, rarely) in one category and the other with drivers who reported never using stay-awake drugs while driving. Selection of predictor variables was based on the variables demonstrated through bivariate analysis to discriminate drug use groups and that were not collinear. Scatter plots were used to test collinearity and outliers.

The factors included in the analysis were length of driving experience (continuous variable), employment category (owner-driver or employee of a small, medium, or large company), whether the driver had an expected time of arrival, the pattern of payment (time based or piece rate), the extent that fatigue was considered a personal problem (major or substantial problem or minor or no problem), and the amount of pay relative to the industrial award for long-distance road transport. In Australia, minimum wages are largely set by industry-wide determinations by government tribunals based on submissions from employer and union organizations. These are known as award rates. The same variables were included as predictors for each survey except expected arrival time, which was not included in the second survey.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 References
 
Bivariate analysis
About one third of drivers in survey 1 and one fifth of drivers in survey 2 reported taking stimulants at least sometimes (table 1). In both surveys, more frequent drug use was associated with being younger, being less experienced, completing significantly more hours of work per week, and being paid based on productivity (by trip or load) rather than on a time basis such as by the hour (table 2). In the first survey, frequent drug use was also associated with working for smaller companies, being paid less than standard rates, and having a scheduled estimated time of arrival.


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  		TABLE 1. Stimulant drug use, age, and work characteristics of Australian long-distance truck drivers by frequency of use reported in survey 1 (1991) and survey 2 (1998)

 

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  		TABLE 2. Company, scheduling, and remuneration characteristics* of Australian long-distance truck drivers by frequency of stimulant drug use reported in survey 1 (1991) and survey 2 (1998)

 
In both surveys, frequent drug users reported that fatigue was a personal problem and they experienced it while driving more often than never users did (table 3). Most drivers in both surveys reported that fatigue made their driving worse, and in the first survey this effect was significantly enhanced for frequent drug users. Additional questions on fatigue and sleepiness were included in survey 2. Compared with never use drugs groups, frequent drug users had significantly higher Epworth Sleepiness Scale scores and reported falling asleep while driving more often (mean Epworth scores: 8.8, 8.2, 7.1, and 6.5 for the four options—often, sometimes, rarely, and never, respectively; F(4,940) = 10.0, p < 0.0001). In both surveys, drivers reported experiencing fatigue after about 12 hours of driving regardless of their exposure to drug use. In both surveys, frequent drug users were more likely than never users to report that they broke road and working-hours regulations (table 4).


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  		TABLE 3. Fatigue experiences and attitudes* of Australian long-distance truck drivers by frequency of drug use reported in survey 1 (1991) and survey 2 (1998)

 

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  		TABLE 4. Frequency of breaking working-hours regulations or road rules* by Australian long-distance truck drivers according to frequency of drug use reported in survey 1 (1991) and survey 2 (1998)

 
Multivariate analysis
For survey 1, the analysis was based on 53.5 percent of cases because of missing data on one (33.9 percent of cases) or more (12.6 percent of cases) variables. The drug use variable was missing for 23 percent of cases (13.4 percent, single missing variable). Examination of the missing data did not show any systematic patterns. For survey 2, the analysis was based on 53.0 percent of cases, with one (36.5 percent of cases) or more (10.4 percent of cases) variables missing. The drug use variable was missing for 12.9 percent of cases (7.1 percent, single missing variable). Again, there were no systematic patterns in the missing data. Analysis of residuals also showed no significant outliers for either survey.

The results for survey 1 (table 5) showed that pattern of payment, amount of pay, experience with fatigue as a personal problem, employment category, and driving experience were all significantly and independently associated with stimulant drug use while driving. Inspection of odds ratios showed that drug use was more than three times more likely for drivers paid on a piece-rate pattern compared with on a time basis (e.g., per hour). Stimulant use was approximately twice as likely for drivers paid less than the award rate, drivers employed by small or medium-sized companies, and drivers who reported fatigue as a substantial or major personal problem. Lastly, less experienced drivers were more likely than more experienced drivers to take drugs.


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  		TABLE 5. Logistic regression model* of factors associated with drug use by Australian long-distance truck drivers reported in survey 1 (1991)

 
For survey 2 (table 6), most of the same factors showed significant associations with drug use. As indicated by odds ratios, piece-rate payment patterns nearly doubled the likelihood of drug use compared with time-based payment patterns. Similarly, drivers who reported fatigue as a substantial or major personal problem were about 75 percent more likely to report drug use while driving compared with those seeing fatigue as a minor or no problem. Less experienced drivers were again more likely to be taking drugs, with an approximately 6 percent decrease in likelihood per year of driving experience.


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  		TABLE 6. Logistic regression model* of factors associated with drug use by Australian long-distance truck drivers reported in survey 2 (1998)

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
References
 
This study showed some important differences related to the use of drugs by long-distance truck drivers. In two independent surveys conducted 7 years apart, the strongest predictors of drug use were payment based on the amount of work completed and fatigue reported as a major problem. In addition, in both surveys, less experienced drivers were more likely to report taking drugs. In the first survey, lower pay and working for smaller companies also predicted stimulant use, adding to evidence for the importance of external factors. These factors encourage drivers to drive long hours despite fatigue.

The strong association of payment by results and low pay with drug use among Australian long-distance truck drivers is consistent with other research suggesting that economic factors are an important influence on health and safety in the workplace. For example, one study showed that higher pay rates and pay increases were related to lower probability of crashes for a large US transport company (11), and another showed that economically vulnerable employers such as small companies may encourage work practices that are less safe and include more high-risk activities (12).

Stimulant use was associated with other adverse outcomes such as poorer compliance with road and working-hours rules and increased likelihood of falling asleep at the wheel. While this finding is consistent with previous studies linking stimulant use and crash risk (2), it is unclear whether stimulant use decreases rule compliance and driving safety or whether the external factors influencing stimulant use also influence compliance and safe driving. When asked the reasons for their noncompliance with rules and regulations, stimulant users were more likely than never users to cite external factors such as tight schedules and economic pressures. This finding lends support to the external-demands explanation. On the other hand, more frequent drug users reported the aftereffects of drug use more often as a reason for breaking road rules. Further research is needed to clarify the relation between drug use and other adverse driving outcomes.

Driving experience was a significant predictor of drug use, with drug use more likely among less experienced drivers. Previous studies of shift workers suggest that long-term shift workers are a "survivor" population; individuals who do not tolerate or adapt to it find other employment (13). In the long-distance road transport industry, drivers who remain in the industry for long periods may be better adapted to the rigors of the job, including long and irregular work hours, and consequently may not need to take drugs.

A possible limitation of this study is its reliance on self-reported measures of frequency of drug use because no objective measures were possible. A number of steps were taken to reduce or measure potential response bias, including encouraging truthfulness through anonymity, not highlighting the stimulant drug use question but embedding it in a list of 16 possible fatigue management strategies, and using interview and self-administration methods and comparing their responses. Response bias was probably minimal since the level of reported stimulant use was similar to that in a previous study of Australian truck drivers (4); similar results were produced by the interview and self-administration versions, and these two independent surveys produced similar results.

In conclusion, finding a relation between drug use and problems with managing fatigue may not be surprising because drivers who have the biggest problem with fatigue might be expected to need to take drugs. The influence of productivity-related payments on drug use is more surprising, especially because this factor had a stronger effect than a range of other factors that could have played a role. This study highlights important implications for designing effective interventions to reduce drug use while driving. The results show that strategies to reduce the use of stimulants in the long-distance road transport industry must focus on reducing fatigue for long-distance truck drivers, but they also show that this goal will probably be achieved only if the external pressures of productivity-based payments are removed from the industry. When drivers are encouraged to complete more trips because they can earn more money, fatigue will be a natural consequence. Stimulant drugs will continue to be used in lieu of sleep; they are one of the few effective strategies available for drivers to stave off fatigue under these circumstances. Changing the incentives for drivers to encourage fatigue reduction is clearly a primary target.


   ACKNOWLEDGMENTS
 
Funding for the surveys was provided by the Australian Transport Safety Bureau and the National Transport Commission. NSW Health funded the current analysis.

Conflict of interest: none declared.


   References
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 

  1. Schwilke EW, dos Santos S, Logan BK. Changing patterns of drug and alcohol use in fatally injured drivers in Washington State. J Forensic Sci (2006) 51:1191–8.[CrossRef][Web of Science][Medline]
  2. Drummer OH, Gerostamoulos J, Batziris H, et al. The involvement of drugs in drivers of motor vehicles killed in Australian road traffic crashes. Accid Anal Prev (2003) 943:1–10.
  3. Crouch DJ, Birky MM, Gust SW, et al. The prevalence of drugs and alcohol in fatally injured truck drivers. J Forensic Sci (1993) 38:1342–53.[Web of Science][Medline]
  4. Mabbott NA, Hartley LR. Patterns of stimulant drug use on Western Australian heavy transport routes. Transport Res Rec Part F (1999) 2:115–30.
  5. Williamson AM, Feyer AM, Friswell R, et al. Driver fatigue: a survey of long distance heavy vehicle drivers in Australia (2001) Canberra, Australia: Australian Transportation Safety Bureau. (Report CR198).
  6. Williamson AM, Feyer AM, Coumarelos C, et al. Strategies to combat fatigue in the long distance road transport industry. Stage 1: the industry perspective (1992) Canberra, Australia: Federal Office of Road Safety. (Report CR 108).
  7. Buysse DJ. Drugs affecting sleep, sleepiness and performance. In: Sleep, sleepiness and performance—Monk TH, ed. (1991) Chichester, United Kingdom: John Wiley & Sons. 249–306.
  8. Gustavsen I, Morland J, Bramness JG. Impairment related to blood amphetamine and/or methamphetamine concentrations in suspected drugged drivers. Accid Anal Prev (2006) 38:490–5.[CrossRef][Web of Science][Medline]
  9. Logan B. Methamphetamine and driving impairment. J Forensic Sci (1996) 41:457–64.[Web of Science][Medline]
  10. Johns M. A new method for measuring daytime sleepiness: the Epworth Sleepiness Scale. Sleep (1991) 14:540–5.[Web of Science][Medline]
  11. Rodriguez DA, Rocha M, Khattak AJ, et al. Effects of truck driver wages and working conditions on highway safety: case study. Transport Res Rec (2003) 1833:95–102.[CrossRef]
  12. Quinlan M, Mayhew C, Bohle P. The global expansion of precarious employment, work disorganisation, and consequences for occupational health: a review of recent research. Int J Health Serv (2001) 31:335–414.[CrossRef][Web of Science][Medline]
  13. Koller M, Kundi M, Cervinka R. Field studies of shift work at an Austrian oil refinery. 1. Health and psychosocial wellbeing of workers who drop out of shiftwork. Ergonomics (1978) 21:835–47.[Medline]

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This Article
Right arrow Abstract Freely available
Right arrow FREE Full Text (PDF) Freely available
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kwm205v1
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