The precision of average annual daily traffic volume estimates from seasonal traffic counts: Alberta example

Investigated in this note is the precision of average annual daily traffic (AADT) volumes estimated from seasonal traffic counts (STC). A large number of road sites located on Alberta's rural highway system were studied. Three frequencies for seasonal traffic counts were considered. They were rotations where the automated traffic recording devices would be active for 2, 3, or 4 selected noncontinuous months of the year. The AADT volume error margins or precision at a 95% confidence level as found in this study are (i) +/-8.00% for 2 noncontinuous month counts during a year, (ii) +/-5.60% for 3 noncontinuous month counts during a year (1993 Alberta program), and (iii) +/-3.61% for 4 noncontinuous month counts during a year. The research can help traffic engineers in carrying out a cost-effectiveness analysis of STC programs, and the precision values such as presented in this research can play an important role in considering a trade-off between the cost and the accuracy of various counts.