What Slows Down a Driver's Reaction Time
Last reviewed: 2026 · Driviology Road Safety Education Team
Quick Answer
A driver's reaction time slows most from fatigue, alcohol or drug impairment, distraction, and, to a lesser degree, age-related changes - each adding measurable delay to how quickly a hazard is actually noticed and responded to.
Reaction time is not fixed - a range of everyday factors can slow it down significantly without a driver necessarily noticing.
The Main Causes of Slowed Reaction Time
Fatigue, alcohol or drug impairment, and distraction are the biggest contributors, each adding measurable delay on top of the baseline described in our guide to reaction time.
The Role of Impaired Driving Specifically
Alcohol and drugs slow reaction time in a way that is well documented and closely tied to the broader risks covered in our guide to impaired driving.
Age-Related Changes
Reaction time can also shift gradually with age, often alongside related changes described in our guide to deteriorating eyesight.