The 'Reaction Distance' is the distance traveled:

Question

Accepted Answer

From when your brain tells your foot to move until your foot pushes the brake pedal.. Section 2.6: Reaction distance is the distance you travel from the time your brain tells your foot to move from the accelerator until your foot pushes the brake pedal (about 3/4 second).

Answer

From when you see a hazard until your brain recognizes it.

Answer

While the brakes are slowing the vehicle.

Answer

While the air builds up.