There are several factors that can affect a person's reaction time while driving in an emergency situation: 1) Distractions like using a phone, eating, or interacting with passengers can slow a person's reaction time by taking their focus away from the road. 2) A person's state of alertness also impacts reaction time - being tired, drunk, or otherwise impaired can lengthen the time it takes to respond to hazards compared to being fully alert. 3) Individual physiological differences like age, health, genetics, and fatigue level can cause reaction times to vary between people even when fully alert. Maintaining alertness and avoiding unnecessary distractions can help ensure the fastest reaction time possible.