LESSON 1/TASK 1
Generalizations based on averages may not be valid. There are three types of averages (mean,
median, and mode). Each of them demonstrates something different. For example, the mean can be
very heavily influenced by extremes. The use of an average may not in fact represent the typical case,
but may have been skewed by one or two isolated instances. For example, one person in a speed
study traveling at an excessively high rate of speed may cause the "average" speed to appear much
higher than what is, in fact, the case. Averages can be helpful in stating typical cases.
Generalizations should not be made on specific incidents without considering other factors. One
example is the speed illustration in the preceding paragraph. Another is that while staggering the work
hours may reduce the peak traffic load, it may increase the overall volume of traffic since it reduces the
number of car pools.
False accuracy may also cause difficulties. If two figures, one accurate and the other an assumption,
are computed together, the result is only as valid as the assumption. The reflected information may not
be accurate.
DEVICES STUDIES
Traffic control devices studies are conducted to ensure that devices are adequate and placed where
they are needed. Initial studies are conducted for the entire installation. These studies are then
periodically updated. The periodic updating may be done on a regular basis, such as weekly or
monthly. It may be based on a specific geographic portion of the installation, or by using routine patrol
reports. When major changes occur in a part of the installation, such studies are also accomplished.
The specifications for traffic control devices in the United States, such as color, shape, size, height,
etc., are contained in the Manual on Uniform Traffic Control Devices published by the Department of
Transportation.
There are three types of traffic control devices: signs, signals, and pavement markings. Pavement
markings are the lines, patterns, words, and other markings set into or painted onto pavement or
curbing. All are used to regulate, warn, or guide traffic. They may be studied individually or in
combination. The studies are conducted to:
o Evaluate conditions.
o Inventory devices.
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