Three basic types of mechanical traffic counting operations are commonly employed by state highway departments to obtain ADT estimates. Hourly recorders are operated continuously at a limited number of locations. Intermittent counts or seasonal control counts are taken four, six or twelve times a year for durations varying from 48 hours to two weeks by far, the greatest amount of traffic data results from short coverage count taken for 24 or 48 hours, but may be as long as five or seven days. In a very few states coverage counts are taken two or four times a year. It is necessary to utilize these coverage counts in arriving at ADT estimates for the many locations on the highway network where continuous recorders and seasonal control stations are not operated.
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