Braking Distance and Safety

Braking Distance – What It Is and How to Calculate It

Braking distance is a crucial factor in road safety and describes how far your vehicle travels from the moment you start braking until it comes to a complete stop. It is important to understand that braking distance can vary greatly depending on several factors, and calculations are intended to provide an estimate – not an absolute truth.

How do you calculate braking distance?

The braking distance can be estimated using the formula:

Braking distance = (speed in km/h ÷ 10)² ÷ 2

Explanation of the formula:

1. Divide the speed by 10: This provides a simple handling of the speed.
2. Square the result: The braking distance increases quadratically with the speed, which means that a higher speed gives a significantly longer braking distance.
3. Divide by 2: This represents an average braking effect on a dry road.

The formula is an estimate and is mainly valid under normal conditions. Actual braking distances may vary depending on the road surface, the condition of the tires and the braking system.

Example: Braking distance at different speeds

Dry road

• 50 km/h: ( (50 ÷ 10)² ÷ 2 = 25 ÷ 2 = 12.5 meters )
• 70 km/h: ( (70 ÷ 10)² ÷ 2 = 49 ÷ 2 = 24.5 meters )
• 90 km/h: ( (90 ÷ 10)² ÷ 2 = 81 ÷ 2 = 40.5 meters )

Slippery road

On slippery roads, the braking distance can be approximately twice as long as on dry roads:

• 50 km/h: ( 12.5 × 2 = 25 meters )
• 70 km/h: ( 24.5 × 2 = 49 meters )
• 90 km/h: ( 40.5 × 2 = 81 meters )

How is the braking distance affected by speed?

The braking distance is affected quadratically by the speed. This means:

• If you double the speed, the braking distance quadruples.
• If you triple the speed, the braking distance is nine times longer.

Example:

• At 50 km/h: The braking distance is approximately 12.5 meters.
• At 100 km/h: The braking distance is approximately 50 meters (quadruple).
• At 150 km/h: The braking distance is approximately 112.5 meters (nine times longer).

Factors that affect braking distance

Braking distance varies depending on several factors:

• Road surface: Wet, slippery or gravel roads can significantly increase braking distance.
• Tire condition: Worn or underinflated tires reduce grip.
• Braking system: ABS (anti-lock braking system) can shorten braking distance and provide better stability.
• Vehicle weight: A heavier vehicle takes longer and takes longer to stop.
• Road conditions: Snow, ice and rain have a drastic effect on braking distance.

A quick method for calculating braking distance

If you need a quick estimate of braking distance, you can use this method:

1. Divide the speed in km/h by 10.
2. Multiply the result by itself.
3. Divide by 2.

Example using the quick method:

• At 50 km/h: ( (50 ÷ 10)² ÷ 2 = 12.5 meters )
• At 70 km/h: ( (70 ÷ 10)² ÷ 2 = 24.5 meters )
• At 90 km/h: ( (90 ÷ 10)² ÷ 2 = 40.5 meters )

The relationship between braking distance, reaction distance and stopping distance

Braking distance is only part of the total stopping distance, which consists of:

• Reaction distance: The distance you travel before you even start braking.
• Braking distance: The distance you travel while braking.

Formula for stopping distance: Stopping distance = Reaction distance + Braking distance

It is therefore important to both pay attention and drive at a speed that allows you to stop safely.

Why is it important to understand braking distance?

Being aware of braking distance makes you a safer driver. It helps you to:

• Adjust your speed: Higher speeds increase the risk of accidents.
• Maintain a safe distance: Understanding braking distance helps you plan your distance to the vehicle in front.
• Be prepared: Understanding how road conditions affect braking distance makes you more aware in traffic.