Stopping Distance and Safe Driving

Stopping Distance – What it is and How it is Affected

Stopping distance is the total distance your vehicle needs to stop from the time you detect a hazard until the vehicle comes to a complete stop. It is a combination of two components: reaction distance and braking distance. Understanding these parts and how they affect stopping distance is crucial to being able to drive safely and adapt your driving to different traffic conditions.

What is stopping distance?

Stopping distance is defined as the sum of:

1. Reaction distance: The distance the vehicle travels from the time you detect a hazard until you start braking.
2. Braking distance: The distance the vehicle travels from the time you start braking until it comes to a complete stop.

The formula for calculating stopping distance is:

Stopping distance = Reaction distance + Braking distance

How do you calculate stopping distance?

To calculate stopping distance, you must first understand the formulas for reaction distance and braking distance.

1. Reaction distance is calculated using the formula: ( \text{Reaktionssträcka} = (\text{hastighet i km/h} ÷ 3.6) × \text{reaktionstid i sekunder} )

This formula explains how far the vehicle travels while you react. Dividing the speed by 3.6 converts it from km/h to meters per second, which is important to get the correct result in meters.

2. Braking distance is calculated using the formula: ( \text{Bromssträcka} = (\text{hastighet i km/h} ÷ 3.6)^2 ÷ (2 × \text{friktion}) )

Here we see that the braking distance increases quadratically with the speed. For example, if you double the speed, the braking distance quadruples. Dividing by 3.6 is also used here to convert to meters per second, and friction affects the braking distance depending on the road conditions.

Once you have calculated both the reaction distance and the braking distance, you can add them together to get the total stopping distance.

Example: Stopping distance at different speeds

Prerequisites:

• Reaction time: 1 second
• Friction: 0.8 (dry asphalt)

| Speed | Reaction distance | Braking distance | Stopping distance | |------------|-------------------------|--------------|--------------| | 50 km/h | ( (50 ÷ 3.6) × 1 = 13.9 meters ) | ( (50 ÷ 3.6)^2 ÷ (2 × 0.8) = 21.7 meters ) | ( 13.9 + 21.7 = 35.6 meters ) | | 70 km/h | ( (70 ÷ 3.6) × 1 = 19.4 meters ) | ( (70 ÷ 3.6)^2 ÷ (2 × 0.8) = 42.3 meters ) | ( 19.4 + 42.3 = 61.7 meters ) | | 90 km/h | ( (90 ÷ 3.6) × 1 = 25 meters ) | ( (90 ÷ 3.6)^2 ÷ (2 × 0.8) = 70.3 meters ) | ( 25 + 70.3 = 95.3 meters ) |

How does speed affect stopping distance?

Speed has a dramatic effect on stopping distance because:

• Reaction distance increases linearly: If you double the speed, the reaction distance also doubles.
• Braking distance increases quadratically: If you double the speed, the braking distance quadrates.

Example:

• At 50 km/h: The stopping distance is approximately 35.6 meters.
• At 100 km/h: The stopping distance is approximately 114.6 meters (more than three times longer).

Important factors affecting the stopping distance

The stopping distance varies depending on:

1. Reaction time: Fatigue, distraction or alcohol and drugs lengthen your reaction time.
2. Road conditions and friction: Dry asphalt has high friction and shorter braking distance, while ice or rain can make the braking distance much longer.
3. Tires and brakes: Worn tires or brakes impair the braking distance.
4. Speed: The higher the speed, the longer both the reaction and braking distance.

The practical importance of stopping distance

Understanding stopping distance helps you to:

• Adjust your speed to suit road and traffic conditions.
• Maintain a sufficient distance from the vehicle in front.
• Avoid dangerous situations by anticipating longer braking distances at higher speeds.