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5 CHAPTER 1 INTRODUCTION 1.1 BACKGROUND: ILLUSTRATIVE EXAMPLE risk relationships for the high-, moderate-, and low-risk subgroups of LSH drivers. In an instrumented vehicle study of local/short-haul (LSH) The risk-exposure odds ratios between the worst and best truck driving sponsored by the Federal Motor Carrier Safety groups of drivers identified here were 12.5 for CIs and 25.5 for Administration (FMCSA), Hanowski et al. (2000) observed high-drowsiness episodes. In other words, on average, each 42 truck drivers driving a total of 28,000 vehicle miles. The high-risk driver in Figure 2 was 12.5 times more likely to study identified 249 critical incidents (CIs), which were be involved in CIs than the low-risk drivers. In Figure 4, the defined as significant unsafe driver actions or "near-crashes." high-risk drivers were 25.5 times more likely to have drowsy Of these 249 CIs, 77 were related primarily to the actions and episodes than were the low-risk drivers. errors of truck drivers. Common critical incidents included There was only a small positive relationship between the running late yellow or red lights and crossing traffic with insuf- rate of CIs and the rate of drowsiness among the 41 drivers ficient gaps (i.e., approaching vehicles too close for safe cross- for which both types of data were available. This suggests ing). The 42 truck drivers initiated 77 CIs in 1,376 hours of that drowsiness was a factor in CI involvement, but it was not driving, yielding an average rate of 0.06 truck driverinitiated a predominant factor. Only one of the six high-CI drivers was CIs per hour. Figure 1 shows the frequency distribution of among the four high-drowsiness drivers. CI/hour rates among the 42 drivers. Of the 42 truck drivers, 6 drivers had CI/hour rates greater than 0.15. These 6 drivers drove 12% of the total driving 1.2 SCOPE hours of the study but were responsible for 38% of all the truck driverinitiated CIs (29 of 77). In contrast, the 25 "best" These LSH study statistics were presented to introduce and of the 42 drivers (the first two bars in Figure 1) drove 63% of demonstrate the phenomenon of high-risk commercial drivers. the driving hours but were responsible for 16% of the CIs. Although commercial drivers generally drive responsibly and Figure 2 illustrates these exposure-risk relationships for the exhibit lower rates of most types of incident and crash involve- "worst" and "best" LSH drivers in terms of CI initiation. ment than drivers in general (FMCSA 2003, Craft 2004, The study also assessed driver alertness level, using a Wang, Knipling, and Blincoe, 1999), it appears that there are 5-point Observer Rating of Drowsiness (ORD) scale, which significant safety-related individual differences among groups had previously been validated against physiological alert- of drivers, and that a few commercial drivers have signifi- ness measures. Levels 4 and 5 corresponded to "very" and cantly elevated risk compared with their peers. "extremely" drowsy. The equipment malfunctioned for one This synthesis will explore individual differences among driver, so there were 41 drivers in this sample. The 41 drivers commercial drivers in general and high-risk commercial driv- had a total of 285 time episodes of Level 4 or 5 on the ORD ers in particular. It will identify dimensions and factors relat- scale over 1,348 hours of driving, for an average rate of 0.21 ing to differences in commercial driver crash risk and assess high-drowsiness episodes per hour. Figure 3 shows the fre- ways that the high-risk driver can be targeted by various safety quency distribution of high-drowsiness episodes for the programs and practices, at both fleet- and industry-wide levels. 41 drivers. Specifically, the synthesis will Four drivers had rates of more than 0.75 high-drowsiness episodes per hour. These four drivers drove 7% of the total Summarize available information on individual differ- driving hours but were responsible for 39% of all observed ences in commercial driver safety performance and high-drowsiness episodes (112 of 285). There was also a alertness. moderate-risk group (10 drivers) who had 29% of the ex- Examine various metrics and tests that might be used to posure and 47% of the drowsy episodes. In contrast, the hire better drivers and avoid hiring high-risk drivers. 27 most alert drivers (the first two bars in Figure 3) drove Identify safety management techniques that are currently 64% of the driving hours but were responsible for only 14% of used by commercial vehicle carriers to target problem high-drowsiness episodes. Figure 4 illustrates the exposure- drivers and their specific risky behaviors.

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6 16 Number of Drivers (N=42) 14 12 10 8 6 4 2 0 .0 .01-.05 .06-.10 .11-.15 .16+ Critical Incident/Hour Groupings Figure 1. Frequency distribution of LSH truck driver critical incident rate. Exposure: Hours of Driving Risk: Critical Incidents 12% 38% 25% High Risk Moderate Risk 46% Low Risk 63% 16% Figure 2. Relationship between exposure and CI risk for high-risk, moderate-risk, and low-risk groups of drivers in the Hanowski et al. (2000) LSH truck driver study. 18 Number of Drivers (N=41) 16 14 12 10 8 6 4 2 0 .0 .01-.25 .26-.50 .51-.75 .76+ High-Drowsiness Episodes/Hour Groupings Figure 3. Frequency distribution of LSH truck driver high-drowsiness episodes.