Hours of service

Hours of Service (HOS) regulations are issued by the Federal Motor Carrier Safety Administration (FMCSA) and govern the working hours of anyone operating a commercial motor vehicle (CMV) in the United States. These regulations apply to truck drivers, commercial and city bus drivers, and school bus drivers who operate CMVs. These rules limit the number of daily and weekly hours spent driving and working, and regulate the minimum amount of time drivers must spend resting between driving shifts. For commerce, the respective state's regulations apply.

The FMCSA is a division of the United States Department of Transportation (DOT), which is generally responsible for enforcement of FMCSA regulations. The driver of a CMV is required to keep a record of working hours using a log book, outlining the total number of hours spent driving and resting, as well as the time at which the change of duty status occurred. In lieu of a log book, a motor carrier may keep track of a driver's hours using Electronic Logging Devices (ELDs), which automatically record the amount of time spent driving the vehicle.

The HOS's main purpose is to prevent accidents caused by driver fatigue. This is accomplished by limiting the number of driving hours per day, and the number of driving and working hours per week. Fatigue is also prevented by keeping drivers on a 21- to 24-hour schedule, maintaining a natural sleep/wake cycle (or circadian rhythm). Drivers are required to take a daily minimum period of rest, and are allowed longer "weekend" rest periods to combat cumulative fatigue effects that accrue on a weekly basis.

Enforcement of the HOS is generally handled by DOT officers of each state, and are sometimes checked when CMVs pass through weigh stations. Drivers found to be in violation of the HOS can be forced to stop driving for a certain period of time, which may negatively affect the motor carrier's safety rating. Requests to change the HOS are a source of contentious debate, and many surveys indicate some drivers get away with routinely violating the HOS. These facts have started another debate on whether motor carriers should be required to use ELDs in their vehicles, instead of relying on paper-based log books.

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