Document Type: Research Paper
Isfahan University of Technology
Transportation Research Institute
A weaving segment occurs where two one-way traffic streams intersect by merging and diverging maneuvers. These segments are considered as one of the most important elements in the freeway capacity and the Level of Service analysis in the Highway Capacity Manual (HCM). Free-flow speed (FFS) plays a major role in this analysis. Hence, the current study used three different methods to compute FFS of a ramp-weaving segment based on field data, and then employed the proposed HCM 2010 model to analyze the weaving segment based on the three FFS values obtained. Ultimately, model results were compared to field data and it was found that the proposed method by the HCM 2010 outperformed the other two methods in field measurement of FFS. However, the considerably poor performance of the presented model by the HCM 2010 in predicting the speed of non-weaving vehicles negatively affected the ultimate performance of the model and caused under-predicted results. Thereby, by applying slight modifications to the field measurement method of FFS for non-weaving flow, this study proposed a novel method which produces significantly more favorable results compared to other methods. The merit of the study becomes even more apparent by considering the context in which manuals like HCM are calibrated in. Traffic models including those mentioned in HCM depend on several contextual factors including vehicle technical characteristics and traffic behaviour. This implies that most recent editions of manuals may not always be the most accurate ones for the traffic condition throughout the highways of Iranian cities.