Stopping Distances Explained: Driven2Drive’s Guide to Safe Driving

Stopping distance is an important consideration when driving and can mean the difference between a safe journey and a hazardous one. However, knowing what’s a safe stopping distance isn’t always intuitive, and there are a lot of factors that contribute to a safe stopping distance. 

In this article, we’ll explore the different elements that go into stopping distance, such as the factors that affect it, external elements, and how to adjust for different driving conditions.

The Basics of Car Stopping Distance

Stopping Distance | Forces & Motion | Physics | FuseSchool

Stopping distance refers to the distance a vehicle travels from the moment the driver brakes until it comes to a complete stop. There are two main components to be aware of: 

1. Thinking distance: In other words, the driver’s reaction time. Thinking distance can depend on various factors such as the driver’s alertness, visibility conditions, and speed.
2. Braking distance: Distance covered until a vehicle comes to a complete stop after braking. This is influenced by factors like speed, a vehicle’s mass, and road conditions.

Given the factors involved in stopping distance, the larger the vehicle, the longer the stopping distance will be. For example, trucks are heavier than cars, meaning there’s more mass to bring to an abrupt stop. For that reason, the stopping distance for trucks is longer than it is for cars. 

What Factors Affect Stopping Distance for a Car?

Understanding the concept of safe stopping is crucial for drivers to maintain a safe distance from other vehicles and to allow sufficient time to react and stop in an emergency situation. Therefore, it’s important for drivers to understand the different factors that dictate a car’s stopping distance.

At Driven2Drive, we make sure all of our students have a fundamental understanding of how their skills, behavior, and attentiveness impact their ability to stop suddenly so that new drivers are as well-prepared for the road as possible. Some of the factors we go over include:

Car Weight

Heavier cars require more force to decelerate compared to lighter cars because the kinetic energy (energy of motion) of a moving vehicle is directly proportional to its mass. A heavier car has more kinetic energy to be dissipated through braking, leading to a longer braking distance.

Car Load

When a car is loaded with passengers or cargo, its weight increases, which in turn affects braking performance. Additional weight adds to the car’s overall mass, which can result in a longer stopping distance.

Car Age

As cars age, different components may experience wear and tear. Brake pads or tires can wear down over time, resulting in less tread and stopping power. To avoid this, make sure your car is regularly maintained and worn-out components are replaced.

Brake Conditions

Brake components such as brake pads, rotors, or brake fluid need to be in good shape for efficient braking. Worn-out brake pads or warped rotors can reduce the friction between the brake system and the wheels, so regular inspections and servicing are important.

Tire Conditions

Worn-out or underinflated tires can reduce the grip between the tires and the road surface, diminishing braking effectiveness. Tires with low tread depth have reduced traction, especially on wet or slippery surfaces, which can increase the braking distance.

What Is the Drivers’ Role in Stopping Distance?

The reaction time for drivers when there’s a hazard on the road is around 0.75 of a second, but can go up to 1.5 seconds for some drivers who might have less experience. Your reaction time is the time between noticing a hazard and taking action, such as pumping the brakes. As a driver, your role behind the wheel is crucial to your stopping distance, and there are several things you can do to reduce your reaction time. 

• Alertness: Being attentive and focused while driving helps drivers quickly detect potential hazards or sudden changes
• Speed and following distance: Adhering to speed limits and maintaining a safe following distance gives you more time and space to brake effectively
• Predictive driving: Scanning the road ahead, observing traffic patterns, and anticipating potential hazards or obstacles, drivers can proactively adjust their speed and position
• Avoiding distractions: Talking on the phone, eating, or playing with the radio can all reduce your focus on the road, leading to a longer reaction time and potentially dangerous situations
• Alcohol: Alcohol impairs your brain’s ability to process information, leading to a longer reaction time. Even a reaction time of a few extra milliseconds or seconds can lead to an accident
• Driving tired: When your brain is tired, its ability to react in time is also affected. Whenever possible, avoid driving until you’ve had enough sleep to drive confidently
• Driver experience: The more experience you have on the road, the more likely you are to react correctly. For example, applying brakes smoothly and progressively, rather than slamming them abruptly, allows for better control of the vehicle and shorter stopping distances

External Factors That Influence Stopping Distance

Factors outside of a driver’s control can also influence stopping distance. Here are some key external factors to be aware of.

• Road conditions: Driving in the snow or on wet, icy roads reduces tire grip. Not only that, but uneven or damaged roads can also affect a vehicle’s stability and braking performance.
• Mountain driving: Steep and winding roads on mountains increase the time it takes for a vehicle to come to a stop. For example, a downward slope puts additional strain on the brakes so drivers need to anticipate and plan for longer stopping distances when in mountainous areas.
• Weather: Weather conditions such as rain, snow, ice, or fog can significantly impact stopping distances. Rain, fog, and snow can affect visibility, requiring drivers to maintain longer following distances and potentially increasing their reaction time.
• Traffic: In congested traffic, drivers often need to maintain shorter following distances, avoid distractions even if traffic is bumper-to-bumper, and be prepared to stop suddenly.

Car Stopping Distances on Dry Roads

There’s a simple formula you can use to calculate the stopping distance:

Thinking distance + braking distance = stopping distance

Here’s an approximation of what that might look like in practice:

Speed	Thinking + braking distance	Stopping Distance
20mph	6m + 6m	12m (40 feet)
30mph	9m + 14m	23m (75 feet)
40mph	12m + 24m	36m (118 feet)
50mph	15m + 38m	53m (174 feet)
60mph	18m + 55m	73m (240 feet)
70mph	21m + 75m	96m (315 feet)

When calculating stopping time, you should always be aware of the average car length and how many projected car lengths you need to stop. The average length of a car is about 4.5 meters (14.7 feet), so when stopping at 20mph, that’s less than 3 car lengths. By contrast, your reaction time at 70mph is about 4.5 car lengths, and it takes you more than 16 car lengths to come to a stop, demonstrating how important speed, following distance, and alertness are when it comes to stopping distances.

Stopping on Wet Roads

When driving in wet conditions, such as in rain, ice, or snow, you need to factor in even more time to come to a full stop. What’s important to keep in mind is that though your reaction time might stay the same, it can take longer to brake. Most of the time, it’s recommended to leave double the distance between your vehicle and the one in front of you, essentially doubling your braking time. 

If we take the same speeds as we mentioned above, here’s how it changes on wet roads:

Speed	Thinking + braking distance	Stopping Distance
20mph	6m + 12m	18m (59 feet)
30mph	9m + 28m	37m (121 feet)
40mph	12m + 48m	60m (196 feet)
50mph	15m + 76m	91m (298 feet)
60mph	18m + 110m	128m (420 feet)
70mph	21m + 150m	171m (561 feet)

Driven2Drive: Get Training to Become a Safe and Better Driver

At Driven2Drive, we understand that knowledge alone isn’t enough, student drivers also need real-world practice to prepare for driving on their own. Stopping distance might seem like a tricky concept to grasp, but by studying it and experiencing real-world applications of how it works, students can become more comfortable behind the wheel and learn how to be a safer driver.

Our lessons combine high-quality driver’s education along with road practice with professional instructors who know how to prepare you for real-world situations so that you know how to best react. 

FAQs

What is the correct stopping distance? 

The correct stopping distance depends on a number of factors, such as the size and mass of your vehicle, your speed, the condition of your vehicle, your alertness level, the weather, road conditions, and more.

What is stopping distance?

Stopping distance is the total distance a vehicle travels from the second the driver applies the brakes until it comes to a complete stop.

What is the formula for braking stopping distance? 

To calculate stopping distance, use the formula Thinking distance + braking distance = stopping distance.