SEASONAL TRAFFIC COUNTS FOR A PRECISE ESTIMATION OF AADT

State and local highway agencies obtain values of traffic parameters such as average annual daily traffic (AADT) from various traffic counting programs. Seasonal traffic counters (STC) are an important traffic monitoring tool, as they supplement the information available from automatic traffic recorders (ATR), providing seasonal, daily, and hourly variation estimates for a particular site or for road segments without ATRs. This study applies several statistical methods to Minnesota highway traffic data to determine the duration and frequency of seasonal counts that can provide precise estimates of AADT at a given statistical confidence level. Previous traffic volume studies for the estimation of AADT have been varied and vague. In this study, AADT estimation errors resulting from different STC schedules are used to develop precision intervals. The authors advise highway agencies that when conducting an STC study, consideration must be given to a tradeoff between various intangibles and the cost of alternative schedules. The estimates of AADT from the STC data are made independent of ATR statistics.