# Braking Distance

Written by Jerry Ratzlaff on . Posted in Civil Engineering

Breaking distance, abbreviated as $$B_d$$ , is the distance that a vehical travels while slowing to a complete stop.

## Braking Distance formulas

 $$\large{ B_d = 1.075 \; \frac{ V^2 }{ a } }$$ $$\large{ B_d = \frac{ 1.075 \; V^2 }{ a } }$$

### Where:

 Units English Metric $$\large{ B_d }$$ = braking distance $$\large{ft}$$ $$\large{m}$$ $$\large{ a }$$ = deceleration rate $$\large{\frac{ft}{sec}}$$ $$\large{\frac{m}{s}}$$ $$\large{ V }$$ = 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.