Last month I wrote about the causes of police involved traffic crashes. Starting this month, our EROC team of instructors will begin presenting a series of monthly articles outlining what officers can do to prevent crashes. We will be focusing, primarily, on providing information that will help officers understand the physical properties which act upon their vehicles while driving; such as friction, momentum, centrifugal force, centripetal force, etc. In other words: Vehicle Dynamics.
One cannot begin to understand vehicle dynamics without first understanding the concept of grip. Grip is defined as: the ability of tires to adhere to the road surface. Grip is a result of friction between the tires and the road surface. Anything that increases this friction enhances grip. Anything that decreases this friction degrades grip. Exceeding the available grip results in a loss of vehicle control.
The portion of a tire that is in contact with the road surface at any time (contact patch) is only about the size of your hand. This small area of each tire is all that provides grip, hence control, to a 4000 lb. patrol vehicle. Therefore, it is critical that we understand how to manage those contact patches.
Grip is affected by three things; the driver, the vehicle and the environment. This month, we will focus on the most important of the three, the driver. The driver is the vehicle’s primary control system. The driver applies inputs into the vehicle controls and the vehicle responds based on those inputs. The problem is if the inputs are faulty, the vehicle’s response will be faulty which greatly enhances the probability of a loss of grip, therefore control. The instructor team at EROC has come up with an easy way for officers to enhance their ability to apply quality inputs into the controls. It’s called the “Three Esses”. Smoothness, Simple dynamics, and Speed control.
Smoothness: Smooth inputs into the throttle, brake and steering wheel are critical to keeping the vehicle balanced. The more balanced the vehicle is, the better the vehicle responds in terms of grip. Coarse steering inputs and harsh throttle and brake application will result in an unbalanced vehicle hence, more potential for a loss of grip (especially as speeds increase). In our EROC training sessions, we like to have the officers imagine a sponge filled with water underneath the throttle and brake pedals. Their job is to think about applying those controls in order to squeeze the water out of the sponge without spraying it all over the cockpit. We also recommend shuffle steering, also known as pull/push steering, when applying inputs into the steering wheel.
Simple Dynamics: This involves asking the vehicle to perform in one plane. In other words, do one thing at a time. Every time the driver puts an input into the controls, weight transfers around the vehicle’s center of gravity. Acceleration causes weight transfer to the rear, deceleration to the front, turning left causes weight transfer to the right and turning right causes it to transfer to the left. Smooth inputs cause the weight to be transferred smoothly, keeping the vehicle in balance, thus enhancing grip. Asking the vehicle to do two things simultaneously, such as braking and turning, causes a diagonal transfer of weight and unbalances the platform. The bottom line is: Accelerate and brake in a straight line; turn without braking or accelerating.
Speed Control: The important thing to remember about speed is: Doubling your speed quadruples the physical forces acting on the vehicle. Each vehicle only has a certain amount of available grip. If we exceed that available grip by carrying too much speed into the wrong situation, we will lose control. A corner that is easily negotiable at 20 mph may very well end in tragic consequences at 40 mph. Under many circumstances, police officers drive too fast…SLOW DOWN!
Here at DriveTeam’s EROC Division, our goal is to provide top quality driver training to police officers. We recommend our ½ day Skid Car training program. DriveTeam uses state of the art skid vehicles to train officers to be proactive in managing grip. To learn more about these safe driving principles, check out our Skid Car program as well as our other advanced courses!
Next month we’ll discuss vehicle and environmental factors that must be taken into consideration in order to avoid crashes.
Until next time, Stay Safe!
Lead Range Instructor
EROC Blue Division