Stopping Distance Calculator
Calculate vehicle stopping distance based on speed, reaction time, and road conditions
Stopping Distance Calculator
Enter the initial speed of the vehicle
Time from perception to brake application (AASHTO recommends 2.5s)
Advanced Settings
Positive for uphill, negative for downhill
Tire-road friction coefficient (0.1 to 1.0)
Stopping Distance Results
AASHTO Formula: s = (0.278 × t × v) + v² / (254 × (f + G))
Speed conversions: 0.0 km/h = 0.0 mph = 0.0 m/s
Road conditions: dry road (μ = 0.7), 0% grade
Example Calculation
Highway Emergency Braking
Scenario: Highway driving at 120 km/h in wet conditions
Given: Average driver (1.5s reaction), wet road (μ = 0.35), flat grade (0%)
AASHTO Calculation
Using: s = (0.278 × t × v) + v² / (254 × (f + G))
Reaction distance = 0.278 × 1.5 × 120 = 50.0 m
Braking distance = 120² / (254 × 0.35) = 161.7 m
Total stopping distance = 50.0 + 161.7 = 211.7 m
Result: The vehicle needs over 200 meters to stop safely
Reaction Time Guide
Friction Coefficients
Note: Actual friction depends on tire condition, road surface, temperature, and other factors.
Understanding Stopping Distance
Components of Stopping Distance
Stopping distance is the total distance a vehicle travels from the moment a hazard is perceived until the vehicle comes to a complete stop. It consists of two main components:
1. Reaction Distance
Distance traveled during perception-reaction time while maintaining constant speed. Formula: d = v × t (where v is speed and t is reaction time)
2. Braking Distance
Distance traveled while decelerating from initial speed to zero. Depends on speed, friction, and road grade.
AASHTO Formula
s = (0.278 × t × v) + v² / (254 × (f + G))
s = Stopping distance (meters)
t = Reaction time (seconds)
v = Speed (km/h)
f = Friction coefficient
G = Grade (decimal)
Key Factors:
- • Speed has quadratic effect on braking distance
- • Road conditions dramatically affect friction
- • Reaction time varies with driver alertness
- • Vehicle weight affects braking performance
Speed Impact on Stopping Distance
The relationship between speed and stopping distance is not linear. Doubling your speed increases the braking distance by approximately four times due to the quadratic relationship in kinetic energy.