In the research project, the influence of heavy vehicles on traffic flow at freeway interchanges was analyzed. The research was based on loop detector data for macroscopic analyses, supplemented by video and radar measurements at heavily trafficked interchanges. Furthermore, selected interchanges were modeled with the microscopic traffic simulation tool BABSIM to analyze the impact of high proportions of heavy vehicles. The empirical and simulated data were used to evaluate the methods in the German Highway Capacity Manual HBS (2015) in particular concerning the values of passenger car equivalents. The analysis showed that the existing methods are generally suitable to cover high proportions of heavy vehicles, but the application of a passenger car equivalent of 2.0 overestimates the influence of heavy vehicles at percentages of 20 % and more. Furthermore, a regression analysis was conducted to identify a function for the estimation of the traffic volume on the rightmost lane. This function was used to generate input values for an analytical model that describes the lane-flow distribution at highway interchanges. Another approach was to extend the procedures for stochastic capacity analysis to model the capacity of merge and diverge areas. The research showed that the stochastic methods are applicable for the analysis of freeway interchange capacity but require a very large data basis, which is not always available. For the microscopic analysis, video and radar measurement data were used to analyze lane changes and headways at interchanges for individual vehicles. The data were collected at different locations to identify the differences during the merging process depending on the distance from the merge or diverge point. The analysis delivered input values for analytical models that were refined concerning the aspect of heavy vehicle traffic. (Author/publisher)
Abstract