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.
Intense lane-changing maneuvers at weaving sections often cause traffic turbulence on expressways, especially in the presence of a concurrent medium exclusive bus lane (XBL) and general purpose lanes. Such intense lane-changing activity usually affects the operation and reduces the capacity of weaving sections in relation to their equivalent basic expressway segments. In this context, a study on the capacity model of weaving areas on an expressway with a median XBL is conducted based on the analysis of lane-change behaviors using gap acceptance theory. Two weaving sections on expressways with median XBL are selected as case studies to obtain the estimated capacity as well as the maximum traffic throughput under a certain bus saturation on the XBL. The results show that estimated capacity is larger than maximum traffic throughput because of low utilization rate of buses on the XBL, and capacity is significantly affected by weaving demand. Error measures based on the estimated and observed maximum traffic throughput are analyzed to verify the validity of the proposed model. A sensitivity analysis shows that, compared with the increase of on-ramp bus flow ratio, the increase of off-ramp bus flow ratio results in a more obvious trend of the reduction of capacity and maximum traffic throughput.
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