Duration of restart period needed to recycle with optimal performance: Phase II

The objective of this research project was to determine the effectiveness, for nighttime work periods, of a restart period containing two biological nights, relative to the 34-hour restart provision in the hours of service regulations governing property-carrying Commercial Motor Vehicle drivers. A sample of 12 healthy subjects was studied in an in-residence laboratory study with frequent testing of cognitive performance and driving performance on a high-fidelity driving simulator. For the primary analysis for this Phase II study, a withinsubjects comparison was made between two 5-day (14-hour/day) nighttime work periods separated by two biological nights operationalized in this study as a 58-hour restart period. For secondary analyses, between-subjects comparisons were made with the data from the preceding Phase I study, in which the restart period was 34 hours in accordance with the present hours of service regulations, and conditions with either daytime or nighttime work periods were examined. In all conditions, subjects were on a daytime schedule during the restart period. The two-night restart provision tested in the Phase II study was more effective at maintaining optimal performance across the two 5-day nighttime work periods than was the 34-hour restart condition with nighttime work periods of the Phase I study, although not as effective as was observed in the 34-hour restart condition with daytime work periods of the Phase I study. This stresses the importance of considering circadian effects on sleep and performance in hours of service regulations, and indicates that depending on the circadian timing of the work periods, a restart period containing two biological nights may be a substantive improvement over a 34-hour restart period with regard to the potential to recycle to the work force with optimal performance.