Under what condition is a driver not allowed to drive, according to federal regulations?

A driver is prohibited from operating a vehicle when they are ill or impaired because this condition significantly affects their ability to drive safely. Federal regulations emphasize the necessity for drivers to be in a condition that ensures the safety of themselves, their passengers, and other road users. Illness or impairment—whether it be due to medications, health conditions, or other factors—can impair judgment, reaction times, and overall driving performance.

While fatigue, feeling unwell, or stress can affect driving performance as well, federal regulations specifically highlight illness and impairment as clear indicators for when a driver should not be on the road. The guidelines aim to ensure that drivers maintain the highest level of fitness while operating commercial vehicles, prioritizing safety for all involved.