The measurement of traffic volumes is one of the most basic functions of highway planning and management. The most accurate measurements of highway demand and highway capacity are calculated at automatic traffic recorder sites which yield the average daily traffic and design hourly volume for the segment of roadway on which it is located. Due to monetary restraints, the majority of roadway segments do not have automatic traffic recorders. For these sites, highway demand and highway capacity must be estimated from short-term traffic counts. This study employed a group of Delaware automatic traffic recorders to determine the fluctuation and seasonality of hourly traffic using statistical techniques. Using short-term traffic counts and an understanding of traffic volume fluctuation, the accuracy of design hourly volume estimates were compared with the true values reported from nearby automatic traffic recorder sites. The study found that design hourly volume estimates were less accurate for roads with greater variability in volume fluctuation, but selection of one method of analysis over another for particular traffic pattern groups resulted in smaller error. On average, the error of design hourly volumes estimates was around 5% for less variable roads and 8-9% for roads with increasing variability.
Abstract