Visual acuity
One of the main effects of speed is the diminishing of foreground objects, which become unclear due to the movement and vibration of the car. Research has shown that this substandard close-up range of vision increases by approximately 20 feet for every 10 mile per hour increase in speed. So at 20 miles per hour we can’t see details clearly 40 feet in front of the car; at 60 miles per hour, not within 120 feet or more.
Let’s imagine a driver with 20/20 visual acuity driving at 60 miles per hour. Further on there is a road sign with three written lines. This driver doesn’t know the zone-his memory can’t be of any help-so he must read the signal. We have seen above that this controller can read 5-inch letters from 280 feet. We now know that when his car reaches a point 120 feet from the sign, he cannot see the details clearly. He has only 160 feet, or 1.8 seconds, to read the signal.
A driver with 20/60 vision cannot see the same sign before reaching a point 93 feet away, but his near vision is affected in the same way as the first driver. Will this controller be able to read a three line message? The problem of reduced near vision explains why some drivers make emergency stops or slow down abruptly at road junctions, especially at superhighway exits. You should always be aware of this danger and be prepared for any sudden actions by other drivers. If you know the area you are driving through, a brief look at the sign will suffice, but remember that strangers who don’t know the way will need longer periods of time.
Highway departments, having studied this problem, use symbols as much as possible, or make the written message as short as possible. Superhighways always have large, easy-to-read signs.
Visual field
His field of vision is reduced by concentration and speed. When you focus on a single object, the field of view is zero, which is often the case with new drivers, because they tend to stare at what they think is important. The field of view also reduces with speed. When stopped, a driver’s field of vision can be up to 190 degrees, but for the same person, the angle will drop to 40 degrees at 60 miles per hour. Therefore, whenever possible, road signs are placed on the road.
judgment distance
Good distance judgment depends on good visual acuity. Since speed reduces sharpness, distance judgment will also be negatively affected when driving fast.
