Capacity Modeling for Weaving, Merge, and Diverge Sections with Median Exclusive Bus Lanes on an Urban Expressway: Microsimulation Approach

Abstract

With the installation of median exclusive bus lanes (XBLs) on urban expressways, understanding of the specific weaving behavior and estimation of the capacity of weaving areas are essential for developing effective engineering measures and operational strategies for expressway management. This study developed an analytical model for estimating the capacity of weaving, merge, and diverge sections with the median XBL installed on an urban expressway by using a microsimulation approach. An in-depth analysis of weaving behaviors was conducted and factors that influenced the weaving section capacity were identified. Specifically, an off-ramp weaving ratio and a newly defined variable called the bus ratio in the total weaving volume were used. A Vissim simulation model was developed and calibrated on the basis of field data collected in Beijing. From the simulation results, a regression model on the capacity estimation was proposed; the model was further validated with a statistical approach and field capacity data. The results demonstrate that the proposed capacity model is applicable and easy to use with an acceptable accuracy. The model can be used not only to estimate the weaving section capacity with a median XBL but also to estimate the capacity of merge or diverge sections with a median XBL under appropriate constraints. Moreover, the proposed model can be applied to examine different bus operational strategies. Hence, a comparative analysis was conducted of the effectiveness of different measures to improve traffic flows in the weaving section with the installation of a median XBL. A recommendation is provided.