What is the primary factor that affects your driving ability when you are not well-rested?

Fatigue is the primary factor that affects your driving ability when you are not well-rested. When a driver is fatigued, their reaction time, concentration, and decision-making abilities are significantly impaired. This can lead to decreased awareness of the surrounding environment, making it harder to respond to sudden changes, such as obstacles or the behavior of other drivers.

While physical health, familiarity with the route, and the quality of the vehicle can all influence driving performance, none of these factors directly relate to mental alertness in the same way that fatigue does. Specifically, fatigue can mimic the effects of alcohol, leading to a higher likelihood of accidents. Inadequate sleep leaves drivers struggling to maintain focus and can lead to lapses in attention, making driving conditions considerably more dangerous.