The objective of this book is to examine the efficacy of the new restart rule promulgated as part of the Hours of Service of Drivers Final Rule. Under the new restart rule, if commercial motor vehicle (CMV) drivers choose to use a provision allowing "restart" of the 60- or 70-hour duty-cycle limit, they are required to include at least two night-time periods (from 1 a.m. until 5 a.m., based on the home terminal time zone if the restart takes place in a time zone that differs from the driver's home terminal) in their restart breaks to allow sufficient opportunity for sleep recuperation before beginning another duty cycle. To investigate the efficacy of this new rule, a naturalistic field study was conducted (before the compliance date) to assess fatigue in drivers working their normal schedules and performing their normal duties. During this study, researchers performed a comparison of driver fatigue between duty cycles preceded by a restart break with only one night-time period versus duty cycles preceded by a restart break with two or more night-time periods. This book discusses the findings of this study.