Braking distance/stopping distance

Braking distance – formula

Braking distance ≈ (initial speed / 10)²

Initial speed is the initial speed of the vehicle in kilometers per hour (km/h). 

This simplified formula is intended to provide an approximate estimate of the stopping distance in metres of a typical light vehicle under normal road conditions.

Another stopping distance formula is the formula provided by AASHTO:

S = (0.278 T V) + V² / (254 * (F + G))

S – stopping distance (in meters)

T – driver reaction/response time (seconds)

V – car speed (km/h)

F – coefficient of friction between the tire and the road. For dry road surfaces – 0.7, for wet surfaces – between 0.3 and 0.4

G – road gradient, expressed as a decimal. It is positive when driving uphill and negative when driving downhill.

However, keep in mind that even after taking the formulas into account, the actual stopping distance may vary due to factors such as :

• road conditions,

• vehicle, tire condition,

• tire type,

• driver reaction time.

Why is it important to understand braking distance?

• You will avoid collisions. Knowing the stopping distance of your vehicle will help you maintain a safe distance from the vehicle in front and reduce the risk of an accident. Also, in heavy traffic, if you brake suddenly, you may be hit by a car behind you. Understanding your stopping and stopping distance is especially important when driving fast, because increasing your speed increases the distance covered during the driver's reaction time, braking distance, and stopping distance.

• Knowing the stopping distance becomes especially important in adverse weather conditions , as road surfaces can become slippery. Drivers must adjust their speed and braking accordingly to maintain vehicle control and avoid collisions.

• KET tests may include questions that define braking distance (from when the brakes are applied to a complete stop) and stopping distance (from the moment the driver sees an obstacle to a complete stop).