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22 20 Number of Drivers 15 (N=42) 10 5 0 .0 .01-.10 .11-.20 .21-.30 >.30 Critical Incident/Hour Figure 9. Frequency distribution of other driver critical incident rates among 42 local/short-haul truck drivers (adapted from Hanowski et al. 2000). besides driving safety; most notably, it is relevant to cargo and for a commercial driver's license (CDL), and specific dis- other operational security. Sixty-one percent of responding qualifying medical conditions (per 49 CFR 391.41) include safety managers check a driver applicant's criminal record, vision and hearing impairment, diabetes, and epilepsy. although this was not rated as among the most effective safety management practices. Checking a driver's credit history has been suggested as a way to assess dependability and stability, 4.4.1 Sleep Apnea but only 21% of safety manager survey respondents reported In the past decade, sleep apnea has been one of the most doing this, and it was rated as the least effective practice of the studied medical conditions in terms of its relationship to crash eight presented. risk. Sleep apnea is a breathing disorder characterized by brief interruptions of breathing during sleep. Among the general 4.4 MEDICAL CONDITIONS AND HEALTH population of drivers, sleep apnea has been shown to increase the likelihood of being involved in vehicular crashes anywhere Driving is a task requiring various physical abilities for sat- from two- to sixfold (see Table 10). That is, drivers with isfactory safety performance. Medical conditions and health sleep apnea are two to four times more likely to have a motor status can have a significant impact on drivers' performance vehicle accident. Further, Young et al. (1993) estimated that if their cognitive, perceptual, and psychomotor skills are approximately 4% of middle-aged male drivers, the predomi- affected. Drivers must pass a medical examination to qualify nant population of truck drivers, may have some form of sleep TABLE 10 Elevated crash risks (odds ratios) associated with various medical conditions per various studies Odds Ratio: Crash Study Sleep-Related Medical Condition Risk Teran-Santos et al. (1999) Sleep apnea (AHI 10) 6.3 Wu and Yan-Go (1996) Sleep apnea 3.0 Young et al. (1997) Sleep apnea: (AHI 5-15) 4.2 Young et al. (1997) Sleep apnea: (AHI >15) 3.4 Connor et al. (2002) Acute sleepiness 11 Masa et al. (2000) Habitually sleepy drivers 13.3 Cummings et al. (2001) Drowsiness 14.2 Note: All studies involved non-commercial drivers. AHI = Apnea/Hypopnea Index (a measure of sleep apnea severity).