Good drivers

Knowledge and a basic understanding of physics and the handling of motor vehicles are the key attributes of good drivers.

What makes a good driver?

An important part of the knowledge that makes a good driver is that of the physical and physiological laws or principles that govern the motion of the car and the driver behind the wheel. The most fundamental of so-called traffic laws are the laws of nature; you can't beat the laws of gravity, friction, force of impact, and centrifugal force.

The entire control of a moving car depends on the grip which four small areas of tire surface have on the roadway at any given moment. These four points of contact are no bigger than the palm of the hand which grips the steering wheel. The coefficient of friction between tires and roadway is itself dependent on many factors, including the condition of the tires, the condition of the brakes and brake pressure, and the kind and condition of the road surface, which is often further dependent on weather conditions. A good driver knows and respects all these conditions. He is also aware of the centrifugal force that operates on curves; this force inexorably tends to push the moving car off the road, just as a rock whirled on a string tends to break the string.

Most important, the good driver is aware of the tremendous amount of kinetic energy developed by a moving car and the real difficulty of changing its motion specifically, stopping the car. Modern engineering genius has made it seem deceptively simple to stop an car. Only when the car collides with something or someone else before stopping is the poor driver jolted into a realization of what a powerful force he was directing.

The kinetic energy packed into the moving car is a function of the weight of the car and the speed at which it is being driven. Speed too high for driving conditions is usually the killing factor in motor-vehicle accidents; it is associated with fatal accidents more than twice as often as any other observed factors. The relationship of speed to death in auto accidents has been worked out by A. N. Kerr, a California mechanical engineer, in terms of danger units. At a speed of 25 miles per hour an car has developed 1 danger unit of kinetic energy. This amount of energy also represents just about the "shock limit" of a human being, the equivalent of a fall from a second-story window.

At 25 miles per hour an car can be stopped within an average street's width, and if it turned over upon hitting an obstacle, it would roll over only once. As speed is increased, danger units increase, but the danger increases faster than the speed. In fact, the danger units are proportional to the square of the speed. Thus, at 35 miles the car packs 2 danger units; at 50 miles, 4 danger units; at 75 miles, 9 danger units. The human body was never engineered to take such shocks.

Just as there are danger units packed in the momentum of a moving car, we can likewise speak of a danger zone always projected in front of it. This danger zone can be easily pictured by imagining the hood of the car stretched out ahead of it for literally hundreds of feet. The good driver is always aware of this danger zone and knows the various factors that determine its length. Both physical and physiological factors are involved. The danger zone is the distance ahead within which the car can be brought to a complete stop.

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