What is the overall braking distance?
The overall braking distance is the total distance a vehicle travels from the moment a driver spots a hazard and decides to stop until the vehicle comes to a complete rest. It equals the thinking (perception) distance plus the braking distance.
In this article, we break down the components, explain how speed and conditions affect them, show rough figures for common speeds, and offer tips to reduce stopping distance.
Two components that make up the total stopping distance
The total stopping distance is made up of two main parts: the distance traveled while you perceive the hazard and react, and the distance your car travels while braking. These parts combine to determine how far your vehicle will travel before stopping.
Two fundamental parts determine the overall stopping distance are:
- Thinking distance: distance covered during the driver’s perception and reaction time. It is approximately speed × reaction time. With a typical reaction time around 1.5 seconds, thinking distance at speed v (in m/s) is v × 1.5.
- Braking distance: distance needed to come to a stop after brakes are applied. It equals v² / (2a), where a is the average deceleration in m/s², which depends on tires, road surface, and braking system. Typical dry-road deceleration is about 7–9 m/s²; wet roads around 5–6 m/s²; icy surfaces can be 1–2 m/s².
In practice, the total stopping distance is the sum of these two components. It increases with speed and worsens with poorer road conditions or slower reaction times.
Typical stopping distances at common speeds (dry conditions)
Below are approximate totals for dry, good-conditions roads with a typical 1.5-second reaction time and standard brakes. Numbers are rough guidelines; real-world distances vary with vehicle and conditions.
- 30 km/h (8.3 m/s): thinking about 12.5 m, braking about 3–4 m, total around 16–17 m.
- 50 km/h (13.9 m/s): thinking about 20.8 m, braking about 10–11 m, total around 31–32 m.
- 60 km/h (16.7 m/s): thinking about 25.0 m, braking about 15–16 m, total around 40–41 m.
- 80 km/h (22.2 m/s): thinking about 33.3 m, braking about 27–28 m, total around 60–61 m.
- 100 km/h (27.8 m/s): thinking about 41.7 m, braking about 42–43 m, total around 84–85 m.
These figures illustrate how quickly stopping distance grows with speed. They also show why small increases in speed can lead to disproportionately larger stopping distances. Always adjust speed to conditions and leave ample following distance.
Factors that affect braking distance
Several variables influence both thinking and braking distances. The most impactful are:
- Speed: Stopping distance increases roughly with the square of speed for braking and linearly for thinking distance.
- Reaction time: Distractions, fatigue, alcohol, and impairment can lengthen thinking distance.
- Road surface and weather: Dry, well-maintained roads with good tires yield shorter distances; rain, snow, ice, or gravel increase them significantly.
- Tire condition and pressure: Worn tires or under-inflated tires reduce grip and raise braking distance.
- Brake system health: Effective brakes, including ABS, improve braking distance; worn brakes reduce performance.
- Vehicle mass and load distribution: Heavier loads or poor weight distribution can affect deceleration.
Understanding these factors helps drivers estimate their own stopping distances and adjust speed and following distance accordingly.
Reducing the overall braking distance
Practical steps to minimize stopping distance and increase safety include:
- Maintain tires with proper tread and correct inflation; replace worn tires promptly.
- Service brakes regularly and listen for signs of reduced braking effectiveness.
- Keep a safe following distance to allow room for unexpected stops.
- Avoid distractions and stay alert to reduce reaction time.
- Drive at appropriate speeds for conditions, especially in rain, fog, or icy surfaces.
- Use appropriate braking technique; in vehicles with ABS, apply steady, hard braking without pumping the brakes.
By prioritizing vehicle maintenance and prudent driving, you can significantly reduce your overall braking distance and improve safety on the road.
Summary
The overall braking distance equals thinking distance plus braking distance. Thinking distance depends on speed and reaction time, while braking distance depends on speed, road conditions, tire grip, and brake efficiency. In dry conditions, stopping distances increase with speed, but adverse weather or poor maintenance can dramatically raise them. Practicing safe speeds, maintaining the vehicle, and keeping adequate following distances are the best ways to minimize stopping distances and enhance safety.
How many car lengths is 100 feet?
100 feet is approximately 6 to 7 car lengths, depending on the size of the vehicle. An average car is about 14.7 feet long, while a larger sedan might be closer to 16 feet, making the range vary.
- Average: Using a mid-size car length of around 15 feet, 100 feet is about 100÷15=6.67100 divided by 15 equals 6.67100÷15=6.67 car lengths.
- Smaller cars: For compact cars that can be 10 to 14 feet long, 100 feet could be up to 10 car lengths.
- Larger cars: For large sedans that are closer to 16 feet long, 100 feet is about 100÷16=6.25100 divided by 16 equals 6.25100÷16=6.25 car lengths.
What is the total braking distance?
Total braking distance, also known as total stopping distance, is the combined distance a vehicle travels from the moment a hazard is spotted to the moment it comes to a complete stop. It is the sum of three components: perception distance (the distance traveled while seeing a hazard), reaction distance (the distance traveled while moving your foot to the brake), and braking distance (the distance traveled after the brakes are applied). Factors like speed, road conditions, and vehicle condition significantly influence total stopping distance.
Components of total braking distance
- Perception distance: The distance a vehicle travels from when the driver sees a hazard until they decide to react.
- Reaction distance: The distance a vehicle travels from when the driver decides to brake until the brake pedal is fully applied.
- Braking distance: The distance a vehicle travels from the moment the brakes are fully applied until the vehicle stops completely.
How it is calculated
- Total Stopping Distance = Perception Distance + Reaction Distance + Braking Distance .
- Perception and reaction distances are often calculated together as "perception/reaction distance".
Factors that affect braking distance
- Speed: Doubling your speed can increase your braking distance by four times.
- Road conditions: Wet or icy roads decrease traction, increasing both reaction and braking distance.
- Vehicle condition: Factors like tire tread, brake condition, and vehicle weight impact stopping distance.
How many feet does it take to stop at 70 mph?
103 feet 245 feet
Time to Stop Your Car
| Speed | Perception/Reaction Distance | Braking Distance |
|---|---|---|
| 50 mph | 73 feet | 125 feet |
| 60 mph | 88 feet | 180 feet |
| 70 mph | 103 feet | 245 feet |
| 80mph | 117 feet | 320 feet |
Is it 2 seconds or 2 car lengths?
The 'Two Second Driving Rule' states that you should remain at least two seconds away from the rear of the vehicle travelling in front of you, regardless of your speed. This will ensure that you will be at least one car's length per five mph away from the car in front, allowing adequate stopping time.
