Sight Distance Calculator

Driver Eye Height ($H_1$): m

Object Height ($H_2$): m

Design Speed (V): km/h

Reaction Time (t): s

Road Grade (G): %

Coefficient of Friction (f):

Stopping Sight Distance (SSD) is the minimum distance required for a driver to see an object and stop the vehicle safely.
It comprises two main components:
- Reaction Distance ($D_R$): The distance traveled by the vehicle during the driver’s perception-reaction time.
- Braking Distance ($D_B$): The distance required to bring the vehicle to a complete stop once the brakes are applied.
The widely accepted formula for SSD (based on AASHTO guidelines) is: $$ SSD = 0.278 \cdot V \cdot t + \frac{V^2}{254 \cdot (f \pm G)} $$ Where:
- $V$ = Design Speed (km/h)
- $t$ = Reaction Time (seconds)
- $f$ = Coefficient of Friction (dimensionless) between tires and road surface.
- $G$ = Road Grade (decimal, e.g., 2% grade is $0.02$). Use ‘+’ for an upgrade (uphill) and ‘-‘ for a downgrade (downhill).