2.6.1 – Stopping Distance Perception Distance + Reaction Distance + Braking Distance = Total Stopping Distance Perception distance. The distance your vehicle travels, in ideal conditions from the time your eyes see a hazard until your brain recognizes it. Keep in mind certain mental and physical conditions can affect your perception distance. It can be affected greatly depending on visibility and the hazard itself. The average perception time for an alert driver is 1¾ seconds. At 55 mph this accounts for 142 feet traveled.