Episode 175 – The Science of Braking

In this week’s Executive Protection and Secure Transportation Podcast, we are talking about the science of braking.

Although most all Security Drivers realize that the higher the car’s speed, the more distance required to stop, what is surprising to many drivers is how much extra distance it takes to stop a vehicle with just a small increase in speed. The braking distance increases four times each time the traveling speed doubles. This is because the work done in bringing a car to rest means removing all of its kinetic energy. So, for a fixed maximum braking force, the braking distance is proportional to the square of the velocity. Huh? Well, I did say the topic is the science of braking. Ok, let’s put this into practical terms.

Listen to the Podcast

Traveling at 20 MPH/ 32.2 KPH, let’s say that the vehicle could stop at 20 Feet/ 6 Meters. If you increase your speed to 40 MPH/64.4 KPH, it will take 80 feet/24.4 Meters to stop. The speed has gone up by a factor of two – from 20 to 40 MPH or 32 to 64 KPH, but the stopping distance has gone up by a factor of four – 20 feet to 80 feet or 6 meters to 24 meters.

The stopping distance is not affected by the method of braking used. It makes no difference if a driver brakes with their left foot – threshold brakes – or uses a parachute to stop. If the speed is doubled, the stopping distance increases by a factor of four. The bottom line is you cannot arbitrarily increase your speed; it’s deadly.

This scientific fact is the reason that when conducting protective driver training, radar guns or onboard computers are necessary for monitoring a student’s speed.  It is not possible for the human eye to detect a difference of two MPH. It is not feasible for an instructor sitting in the passenger seat to determine the difference between 2 MPH or 3 KPH, yet that small difference in speed can mean the difference between avoiding an incident or not.

As a side note – Do Not Threshold Brake with an ABS Vehicle. With a vehicle equipped with Antilock Braking System, press as hard as your foot can press and let the computer do its job. This topic will be covered in a future episode.

With an ABS vehicle, all it takes is that first hard application of the brakes, and the computer takes over. But for the computer to operate at max efficiency, the brake pedal must be pressed as hard as possible. In many instances, the driver does not accomplish this with the first application of the brakes; in fact, a driver presses semi-hard on the brakes and then increases the pedal pressure as the object they are trying to avoid gets bigger in the windshield.

The Connection

When confronted with an emergency, the vehicle’s braking, steering, and gas pedal controls are all connected. How much you can move the steering wheel depends on the speed of the vehicle. The lower the speed, the more you can move the steering wheel. It is important to understand that the sooner and harder you apply the brakes, the more you can turn the steering wheel.

Also, in many emergencies is not only how quickly you can stop but how much speed you can take off the car as quickly as possible. For example, the numbers that follow are used for explanation purposes; these numbers can vary depending on various conditions, but the theory is valid.

There are many variables involved, but it is the theory that is important.

If an ABS vehicle is traveling 50 MPH / 81 KPH and the brake pedal is applied as hard as possible, a half of a second later, that vehicle will be moving at the rate of 40 MPH – 64 KPH, and a second later, that vehicle would be moving 28 MPH – 45 KPH. The point is that the initial emergency occurred at 50 MPH; at that speed, you have X amount of steering available before the vehicle loses control. Suppose the brakes are applied as hard as possible a half a second later. In that case, the vehicle is moving 40 MPH – 64 KPH, providing the driver with X plus steering to get out of trouble, and a second later, the vehicle is traveling 28 MPH – 45 KPH, giving the driver X plus steering to get out of trouble.

Keep in mind the lower the speed, the more you can move the steering wheel.

If you were driving at 60 MPH – 97 KPH and applied the brakes hard, using all of the vehicles braking capability with a Coefficient of Friction of .8 the results would be:

Slow the car down as much as you can as quickly as you can.

An emergency most always requires not only slowing the vehicle; it will also require steering. The quicker you lower the speed, the more steering you have to avoid the problem. It is simply an exercise in the science of driving.

This scientific phenomenon or fact can easily be demonstrated to students or for your benefit as an instructor or just to gain knowledge.

If a Radar Gun is used in the training process, this scientific factoid can be demonstrated. When conducting training, the instructor should be looking at their radar gun. This concept can demonstrate this by pointing a radar gun at the vehicle as it enters the braking exercises and notices how quickly the speed drops. You can look at the radar gun and get an indication of how hard the student applied the brakes. If done properly, the speed indicated on the radar gun will drop significantly within the first second.

Some Notes

Braking is one of the most important skills to learn because brakes are the vehicle’s most powerful control. Society of Automotive Engineering studies has shown that most accidents are caused because of improper braking. Although there are no statistics that can prove this, we would say that the same is true of vehicle attacks.

Definition of Emergency Braking

Emergency braking is a time-distance relationship. A braking emergency is the absence of enough time and distance to stop or maneuver the vehicle out of a problem. Although this may sound simplistic, if there were enough time and distance to stop, it wouldn’t be an emergency. 

Brakes are the most powerful control in the vehicle

The brakes produce larger changes in speed than accelerating. They can easily overwhelm the most powerful engine. It takes more time to go from 0 to 60 MPH – 96.6 KPH than it does to stop from 60 MPH / 96.6 KPH to 0.

Time to reach the brakes

Training providers should emphasize the amount of time it takes to reach the brake pedal in an emergency and translate that time into meaningful distance figures applicable to the students’ speeds in their exercises.

Look Where You Want to Go

A significant component of braking to avoid an emergency has nothing to do with braking; it’s all about where you look while the emergency is unfolding. Car manufactures have been studying this phenomenon for a while. Simply stated – your hands go where your eyes look. As soon as the emergency presents itself, look for a place to put the vehicle. Look where you want the vehicle to go, and your hands will follow your eyes. Often, the driver’s eyes fixate on the object they are trying to avoid, and the result is they drive into it. By the way, this is not as easy as it sounds.

Summary

  1. Be careful about increasing speeds – for every 10% increase in speed, it is a 20% increase in stopping distance.
  2. When confronted with an emergency with an ABS vehicle, press the brake pedal as hard as possible.
  3. The sooner and harder the brake is pressed, the lower the speed, and the lower the speed, the more you can move the steering wheel
  4. In an emergency braking scenario, look where you want to put the vehicle.

If you have an interest in going much deeper into these types of topics, I invite you to check out the International Security Driver Association’s website ISDACenter.Org and consider joining the membership to gain access to the encyclopedia of executive protection and secure transportation – The ISDA knowledge center.

The knowledge shared encompasses a wide range of executive protection and secure transportation focused topics with resources, information, and metrics.

For more information on all of the member benefits, head over to https://isdacenter.org.

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