Studies have shown that ______ drivers tend to fatigue at a rate much faster than ________ drivers.

• A. Nighttime fatigue faster than daytime drivers
• B. Daytime fatigue faster than nighttime drivers
• C. Both fatigue at the same rate
• D. Fatigue rates vary independently of time of day

Answer: (A)

Alertness follows a circadian rhythm, with a natural low point at night. Driving during these nighttime hours confronts you with that inherent dip in wakefulness, plus any sleep debt, which makes fatigue rise more quickly. Because of this circadian trough, nighttime drivers tend to fatigue at a faster rate than daytime drivers.

The other ideas don’t fit the pattern supported by research. Fatigue during the day isn’t typically faster than at night, and saying fatigue rates are the same regardless of time of day ignores the well-established influence of the circadian cycle. Likewise, claiming fatigue rates vary independently of time of day contradicts evidence that alertness levels are modulated by time of day.