Statewide Traffic Volume Studies and Precision of AADT Estimates

Abstract

Investigated in this paper is the statistical precision of annual average daily traffic (AADT) estimates resulting from short period traffic counts (SPTC). A large number of automatic traffic recorder (ATR) sites located on Minnesota's highway system are studied. Effects of various factors on estimation errors are investigated. The appropriateness of volume adjustment factors is expressed in terms of assignment effectiveness, which reflects the degree of correctness with which a sample site is assigned to an ATR group. Among several other conclusions, it is found that AADT estimation errors are very sensitive to the assignment effectiveness. The study results suggest that highway agencies should put more emphasis on sample site assignments to correct ATR groups than on the duration of count, i.e., whether it be a 24-, 48-, or 72-hr traffic count. The main study findings are confirmed by analyzing ATR data from two Canadian provinces, namely, Alberta and Saskatchewan. It is believed that the material presented in this paper can be beneficial to highway agencies in the rationalization of their traffic volume counting programs.