Statewide Traffic Volume Studies and Precision of AADT Estimates

Abstract

Investigators examined the statistical precision of annual average daily traffic (AADT) estimates derived from short period traffic counts (SPTC). Many automatic traffic recorder (ATR) sites located on Minnesota's highway system are studied. Effects of various factors on estimation errors are explored. The appropriateness of volume adjustment factors is expressed in terms of assignment effectiveness, which mirrors the degree of correctness with which a sample site is assigned to an ATR group. Investigators found that AADT estimation errors are very sensitive to the assignment effectiveness. Study findings indicate that highway agencies should put more emphasis on sample site assignments to correct ATR groups than on the duration of count. By analyzing ATR data from two Canadian provinces--Alberta and Saskatchewan--the findings are confirmed. Highway agencies may find the material presented in this paper beneficial in the rationalization of their traffic volume counting programs.