Design Hourly Volume Estimation at Freeway Nodes from Short-Term Traffic Counts

This paper extends the concept of a design hourly volume (DHV) which is derived from the ‘nth hour’ to a concept based on the nth highest saturated hour. To calculate this nth highest saturated hour at each ramp junction of a node, permanent traffic counts (PTC) are necessary on all ramps and the main lanes. In practice, such counts are often not available. For such cases, the German HCM proposes a method that enables the estimation of the design hourly volume through short-term traffic counts (STC) and the extrapolation of the results using available PTC in the vicinity. Within the scope of this study, it is examined how accurate the required nth highest saturated hour can be estimated with this method and similar concepts. Furthermore, it is investigated to what extent the number and the location of the available PTC affect the accuracy of the estimation. Scenarios without PTC are also considered. The evaluation is based on a database with a total of 72 freeway nodes for which PTC data from three years (2017-2019) are processed. The results show that the estimation of the nth highest saturated hour with the method of the German HCM works accurately, even if only one PTC is available on each inflowing approach. ... mehrThe results further indicate that STC are crucial to achieve accurate results when only few PTC are available. Acceptable results are also obtained by STC of one week, even without a projection at a PTC.