Document Type

Working Paper

Publication Date



Vehicle detectors -- Oregon -- Evaluation, Traffic flow -- Analysis, Traffic estimation, Automatic data collection systems, Oregon Department of Transportation

Physical Description

34 pages


Traffic volume data are needed for design and construction zone traffic management. In addition, continuous traffic volume data (collected by automatic traffic recorders) is needed to factor short counts (24 hours or more) collected at key sites on the states highway network.

This study evaluates the procedures used by the Oregon Department of Transportation for collecting continuous traffic volume data to determine: (1) if the current location and number of automatic traffic recorders (ATRs) on Oregon's highway network is adequate for estimating monthly seasonal factors, and (2) if the current procedure of using group means, based on geographical regions, to calculate seasonal adjustment factors is the best method. The use of simple regression versus (1) cluster specific means from computer generated clusters, and (2) weighted means based on the distance from one ATR to the three closest ATRs that triangulate the point, are evaluated as techniques for calculating monthly seasonal adjustment factors from ATR data. These adjustment factors are used to factor volume data where only short counts are available. The results show the current geographical location of ATRs used by ODOT compare favorably, statistically, with other siting criteria. However, it is shown that the task of factoring short count data for making inferences about traffic volume count data from known locations to unknown locations on the highway network can be improved by siting additional ATRs in high volume, small urban areas. In addition, two new areas of research are addressed which have application to real time integrated traffic data collection.


Catalog Number DP91-3.

A product of the Center for Urban Studies, College of Urban and Public Affairs, Portland State University.

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