PREDICTIONS OF DESIGN HOUR VOLUME AS A FUNCTION OF AMOUNT AND NATURE OF TRAVEL

This article which discusses the estimation of design hour volume (DHV) from sample traffic counts, describes an investigation which attempted to: 1) reexamine the commonly used 30HV-AADDT relationship; (2) propose an alternative model to predict the DHV from sample traffic counts and compare it with the 30HV-AADT (average annual daily traffic) model; and (3) reexamine the nature of K-factor (ratio of DHV to AADT) with respect to the type or nature of travel and the AADT volume. The study found that when a single 30HV-AADT relationship is developed for the entire highway population, systematic errors of prediction result, even when the coefficient of determination for the equation is very high. The prediction results improve significantly when the 30 HV-AADT relationships are developed for segregated groups of roads. Although the grouped models generally result in better prediction than ungrouped models, they may still be subject to significant errors of th 30HV estimates. The findings of the study are discussed in detail.