# Stopping Distance Calculator

Our stopping distance calculator will tell you **how long a moving car will travel before it comes to a stop**.

Finding the stopping distance is a key factor in car safety research 🚗, and in this short article, we will explain everything you need to know about it, including:

- Braking distance and stopping distance difference;
- Braking distance formula;
- The stopping distance formula; and
- How to calculate stopping distance.

## Braking distance and stopping distance

We should consider two similar definitions when calculating the distance before a car stops: the *braking distance* and the *stopping distance*.

The **braking distance** is * the distance a moving car travels from when the driver presses the brakes to when the vehicle stops moving*.

Similarly, we define the **stopping distance** as * the distance between the moment the driver notices an obstacle* (such as an animal crossing the road)

**and reacts by pressing the brakes and the instant the car stops moving.**Here, the key difference is the driver's perception-reaction time, which we account for in the stopping distance formula.

💡 You can also obtain braking times using the `advanced-mode`

of this stopping distance calculator by inputting the deceleration of the brakes.

## Stopping distance formula

If you want to know how to calculate the stopping distance, **AASHTO (the American Association of State Highway and Transportation Officials)** gives us the stopping distance formula which is used in road design to protect the drivers:

where:

- $s$ is the
**stopping distance**in meters. - $t$ is the
**perception time**in seconds. You can read more about perception-reaction times values in the following section. - $v$ is the
**car's****speed**in km/h. - $G$ is the
**grade of the slope**, which is positive for**uphill**and negative for**downhill**(leave as 0 for flat roads). - $f$ is the
**coefficient of friction**, which is assumed to be`0.7`

on**dry roads**and between`0.3`

and`0.4`

on**wet roads**.

🙋 Too complicated? Just fill in the parameters in our stopping distance calculator, and it will automatically do the work for you!

If we don't account for **perception-reaction times** or **road inclination**, we get the **braking distance formula**, which uses the same parameters:

## Perception-reaction times

Our stopping distance calculator allows you to input any perception-reaction times. However, it would be best if you had some values as guidelines:

- 1 second - A keen and alert driver.
- 1.5 seconds - An average driver.
- 2 seconds - A driver who is tired or an elderly person.
- 2.5 seconds - Worst case scenario. Even elderly or intoxicated drivers will probably manage to react within 2.5 seconds.