The calculation of braking distance:

s: total braking distance [m] (s=s_R+s_F)
s_R: perception reaction distance [m]
s_F: braking deceleration distance [m]

Perception reaction distance:

s_R=(v/3.6)t_R/3.6

v: speed of vehicle [km/h]
t_R: reaction time [s]

To reduce the kinetic energy to zero:

µmgs_F=m(v/3.6)²/2

µ: coefficient of friction [ ] (between the tires and the road)
m: mass of vehicle [kg]
g: acceleration of gravity [9.81 m/s²]

it follows:

s_F=(v/3.6)²/2µg=0.004v²/µ

The total braking distance:

s=s_R+s_F

A. reaction
B. perception
C. decision
D. action

Possible values:

µ: coefficient of friction [ ]:

new tire, dry road: 0.85-0.7
new tire, wet road: 0.65-0.2
worn tire, dry road: 1.0-0.9
worn tire, wet road: 0.5-0.1
snow, ice: 0.1 and less

reaction time [s]: 0.5-2.5

Calculated values:

conditions of calculation:

horizontal road
µ= 0.5 (medium adhesion between the tire and the roadway)
t_R= 1.5 [s] (medium reaction)

Calculated results:

visibility/color of clothing:              braking distance/speed:

Distance at which driver first see pedestrian

1. dark clothing (black, blue)
2. red clothing
3. yellow clothing
4. white clothing
5. wearing reflectors

Based on Cornell University Cooperative Extension Program Report "Actionwear: Clothing for Fitness."