United States Department of Transportation
i
Assessing Roadway Traffic Count Duration and Frequency Impacts on Annual Average Daily Traffic Estimation: Assessing Accuracy Issues Related to Annual Factoring
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2016-01-01
[PDF-817.22 KB]
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Abstract:Annual average daily traffic (AADT) for many roadways is estimated through a temporary count obtained over anywhere from a few hours to one week, and subsequently expanded to a full year using factors derived from permanent count stations with similar characteristics. Many organizations perform these counts less than annually and therefore must further adjust counts from a prior year (typically 1, 2, or 5 years prior, depending on the roadway type) to the current year. This task quantifies the relative accuracy and precision associated with different annual count cycles for 24- and 48-hour count durations. Results are evaluated at the national level, as well as by functional classification of sites, and at the individual state level. The FHWA Travel Monitoring Analysis System (TMAS) volume data from 14 years consisting of hourly counts by day from nearly 6,000 continuous permanent volume traffic data sites/years in the United States comprised the reference dataset for this research. A subset of 320 of these were utilized which include complete data for all 24 hours of every day of the year. These sites collectively represented a wide range of AADT volumes, 9 functional classes, 32 states, and years 2000 through 2012. This report is a final task report that summarizes accuracy and precision of expanding short-term counts' Average Daily Traffic (ADT) to AADT, depending on the frequency with which the counts are obtained (yearly, every two years, every three years, or every six years), and includes the analysis methodology and summary statistics findings.
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