Police officers, by the nature of their job, must to be in control of their environment. The environment in which many of us spend a large part of our work day is our patrol vehicle. It is imperative, as emergency vehicle operators , that we understand the importance of maintaining 100% control of our patrol vehicle, 100 % of the time. There should never be a situation in which we do something to create a loss of control. Just like we must be in total control of our weapon systems, we must control the massive amount of energy produced by our patrol vehicles. A Glock .40 caliber pistol launches a 180 grain projectile at about 1000 feet per second (about 665 miles per hour) and produces about 400 foot pounds of energy at the muzzle. A 4000 pound patrol vehicle traveling at 90 feet per second (60 miles per hour) produces nearly 500,000 (one half million) foot pounds of energy!
The understanding of vehicle dynamics and how the operator can control those dynamic forces can go a long way in helping to maintain control of the energy produced by our patrol vehicles. Our Emergency Response Operations Courses (EROC) here at DriveTeam, teach that the 80% Rule is the #1 rule of controlled driving. Simply stated, the 80% rule means that the operator of a patrol vehicle should NEVER exceed 80% of their vehicle’s capability nor should they EVER exceed 80% of their own skill level. This month we’ll discuss managing vehicle capabilities.
Our primary focus in our EROC courses is to help the operator learn their vehicles’ capabilities and to improve their skill level. Our driving exercises are designed to gradually bring drivers up to the vehicle’s 80% level while, at the same time, analyzing and correcting driving techniques so that the operator’s skill level can be improved.
The understanding and recognition of the 80% level is crucial. When the vehicle is pushed beyond 80% of its physical capabilities, the margin of error shrinks very rapidly. If an operator is driving at 100% of a vehicle’s capability, there is virtually ZERO margin of error. Between 80% and 100% the forces on the vehicle ramp up extremely fast. This is due to the fact that as vehicle speed doubles, the forces acting on the vehicle quadruple.
Many modern patrol vehicles have cornering capability, under ideal conditions, of approximately 0.80g’s+/- of lateral force pushing the vehicle to the outside of a turn. The vehicle’s tires push back in an effort to counter this force. If the force pushing the vehicle to the outside of the corner overcomes the tires ability to push back, a loss of control results.
Notice the effect of these forces in the following example:
Let’s drive our vehicle around a 100 foot radius corner at 25 mph. Our vehicle is now generating about 0.40g’s of lateral force pushing it to the outside of the corner. We will easily make it around the corner because it is generating less than half of the force which the tires are capable of resisting. Doubling the vehicle’s speed to 50 mph around the same corner (25×2) produces 1.60gs’ of force pushing us to the outside of the curve (0.40×4). The results will be predictably disastrous, for we are now asking the vehicle to exceed 2 times it’s cornering capability (1.60g’s vs 0.80g’s). If we drive at 100% of the vehicles capability(0.80g’s) we would negotiate the same corner at about 35 mph with absolutely no margin of error. Operating the vehicle using the 80% maximum rule we could negotiate the corner at0 .64g’s at about 31 mph and still have a safe margin of error. As can be seen, the difference between not making the corner and safely negotiating the corner is only a few miles per hour. There is nothing wrong with taking the same corner under 80%. Remember, 80% of the vehicles capability is our MAXIMUM.
The “double the speed, quadruple the force” formula applies to straight line velocity and braking also. Our 4000 lb. patrol vehicle, moving forward at 25 mph, produces about 88,000 foot pounds of energy. Increasing our speed to 50mph. now produces about 352,000 foot pounds of energy – four times as much as at 25mph. Braking from 20 to zero mph. should take about 32 feet to for the average patrol vehicle to accomplish. Braking from 50 to zero mph will take about 128 feet. This does not include driver reaction time. As can be seen, too much speed in the wrong place greatly increases the probability of things turning out badly.
How do we know if we are coming close to exceeding 80% of our patrol vehicle’s capability? Experiencing vehicle responses during training is the most important factor. Our Essential and Advanced EROC courses are specifically designed to gradually approach 80% of the vehicle’s capability and then complete a series of repetitions at the 80% level. Changes in the vehicle’s responses are discussed between runs. Drivers successfully completing 80% runs are next encouraged to drive at upwards of 90% to 100% of the vehicles capability in order to experience vehicle responses at the very limits of control or lack thereof. More 80% runs will follow. Debriefings and comparisons of vehicle responses are made. At the end of the training day officers will have a much stronger understanding of what their specific patrol vehicle can and cannot do.
Next month we’ll spend some time discussing the 80% rule as it applies to the driver.
Check out our Fall 2016 Essential, Advanced, Pursuit, Winter Skills and Pursuit Supervision Courses. Above all, Stay Safe!
Dave Schultz
Senior Range Instructor
EROC Blue Division
DriveTeam Inc.