The investigators are aware that there are some intrastate truck drivers who may be under age 21, however they are a much smaller and different population. By definition they are not long-haul drivers, tend to have more job instability, have a different occupational environment that is relevant to this study (e.g., sleep at home), and thus are a different population that this research does not target. Thus, this study has sound rationale for not including children ages 18-20.