LESSON 1/TASK 1
Photographic and video techniques can be extremely valuable. They provide an additional means of
analyzing traffic studies. They are also effective in showing before and after views of a situation. All
techniques should be considered. They include both still and motion photography. Modern
photographic technology can provide light and easily used equipment compared to the older, more
cumbersome equipment. Consideration should also be given to the use of aerial as well as ground
views.
Common Problems
The purpose of making a study is to find answers to a problem. The person analyzing study results
must guard against mistakes through oversimplification or looking for the easy answers. The following
paragraphs discuss some of the more common mistakes and tendencies that may skew the results of
traffic studies.
The failure to evaluate and/or explore all available information is a common error.
There are four types of fluctuations that affect traffic studies. All should be considered to ensure that
the results are not skewed or data misinterpreted.
o Long term trends which are not affected by short term changes must be noted.
o There may be fluctuations above and below a long term trend line. These fluctuations may be
caused by short term changes or other factors.
o Seasonal changes, as well as the effects of the time of day or month, may affect volume, speed,
and accident data.
o Chance variations may also cause misinterpretations during short term studies. This is called
the "spatter effect."
The person doing the analysis may use faulty reasoning. Some of the more common pitfalls in this
area are discussed in the following paragraphs.
The use of an unjustified assumption concerning cause and effect. There is a difference between two
events being correlated and cause and effect. Just because one event almost always precedes
another does not mean that it is the cause of the second event.
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