Daily Effective Circulation (D.E.C.) is the average number of passers-by or persons (18+ years) in cars or other vehicles, that could potentially be exposed to an advertising display or billboard for either 12 hours (unilluminated – 6:00am to 6:00pm) or 18 hours (illuminated – 6:00am to 12:00 midnight) on an average day. Many billboard operators use actual traffic counts provided by State departments of transportation (or DOTs) since most people understand this well in given market areas. The equation to calculate Daily Effective Circulation for a particular billboard equals the number Adults (18+ yrs.) multiplied by the effective illumination rate of the display or billboard multiplied by the average passengers in a car or other vehicle.
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