Analytical Procedures for Estimating the Capacity of the Urban Expressway Section near Off-Ramps and On-Ramps with a Median Exclusive Bus Lane

Abstract

This paper presents a microsimulation approach for developing the analytical procedure for estimating the capacity of the urban expressway section near off-ramps and on-ramps with a median exclusive bus lane (XBL). First, with a thorough analysis of the operation caused by the installation of median XBL, three factors that influence the capacity are identified. Then, a microsimulation framework is developed. Regression analysis of factors influencing the capacity is conducted for the median XBL based on the results of the microsimulation. Further, simulation experiments on capacity estimation under different scenarios are designed. Finally, the analytical model on the capacity reduction factor is established, which considers the impact of both roadway allocation from XBL and more complex interference due to the installation of XBL. A randomly chosen section with the off-ramp and on-ramp along the third ring road in Beijing is used to validate the proposed model. Because there has not been an XBL installed on the ring road expressway, a simulation model is developed for this chosen section, in which the median XBL is installed and the capacity is calculated by the proposed model. The results are compared with those from the simulation model, demonstrating that capacities obtained from the proposed model are close to the simulated ones with small relative errors. Further, a field location on Jingtong Expressway is also chosen and field data are collected for comparison with the results from the proposed model. Small relative errors are also observed. Thus, the proposed model is shown to provide a practical estimation for the capacity of the urban expressway section near off-ramps and on-ramps with a median XBL.