In Australia, default hourly traffic flow histograms are used in models for estimating savings to road users from road improvement proposals. This report describes the development and updating of hourly traffic volume frequency distributions for use in estimating road user costs as part of the economic evaluation process for road investment proposals. The report concludes that the use of hourly histograms (grouping the 8,760 hours in a year into a number of flow categories) is appropriate, that the accuracy of estimated congestion effects is improved by moving from 4 percent to 2 percent class intervals, or by using averages representing each histogram bar rather than midpoint values, and that separate computation for each carriageway on divided roads gives improved results. Existing permanent traffic counting stations were found to be capable of providing the data necessary to develop and update default histograms. Further investigation is suggested of variations in traffic composition with flow. New histograms were developed from recent traffic count data in Victoria, South Australia, Tasmania and Queensland. (Author/publisher)
Abstract