# Brake Reaction Distance

Written by Jerry Ratzlaff on . Posted in Civil Engineering

Brake reaction distance, abbreviated as $$B_r$$, is the distance traveled from the point of detecting a hazard until you begin braking.

## Brake reaction Distance formula

 $$\large{ B_r = 1.47 \; V \; t }$$

### Where:

 Units English Metric $$\large{ B_r }$$ = brake reaction distance $$\large{ft}$$ $$\large{m}$$ $$\large{ t }$$ = brake reaction time $$\large{mi}$$ $$\large{mi}$$ $$\large{ V }$$ = design speed $$\large{\frac{ft}{sec}}$$ $$\large{\frac{m}{s}}$$

## AASHTO Exhibit 3-1 Stopping Sight Distance

 Design Speed Brake Reaction  Distance Braking Distance  on Level Stopping Sight Distance Calculated Design 15 55.1 21.6 76.7 80 20 73..5 38.4 111.9 115 25 91.9 60.0 151.9 155 30 110.3 86.4 196.7 200 35 128.6 117.6 246.2 250 40 147.0 153.6 300.6 305 45 165.4 194.4 359.8 360 50 183.8 240.0 423.8 425 55 202.1 290.3 492.4 495 60 220.5 345.5 566.0 570 65 238.9 4.505 644.4 645 70 257.3 470.3 727.6 730 75 275.6 539.9 815.5 820 80 294.0 614.3 908.3 910 Note:  Brake reaction distance predicated on a time of 2.5 s; deceleration rate of 11.2 $$ft/s^2$$ used to determine calculated sight distance.