The strategy of providing exclusive bus lanes on urban expressways is receiving increased policy attention, especially in China. However, one important question to be answered before such strategy is put into implementation is what impact the strategy will have on the capacity of the expressway, especially on that of weaving sections caused by exclusive bus lanes. This paper is intended to present a microscopic traffic simulation approach to the capacity analysis of weaving sections caused by the installation of exclusive bus lanes on urban expressways. The paper first identifies three different kinds of exclusive bus lane configurations in Beijing, including median bus lane with off-on-ramp, curbside bus lane with on-off-ramp, and curbside bus lane with off-on-ramp. Then, the weaving section length, headway, mainline volume, and off-ramp and on-ramp volumes for general traffic are considered as the primary parameters in designing simulation scenarios. Subsequently, the microscopic traffic simulation is executed, by which the capacity of the weaving sections is estimated and the impact of the weaving section length and headway on the capacity is evaluated. It is found from the analysis that the weaving section length and headway have different impacts on the capacity for general traffic for different kinds of exclusive bus lane configurations. Further, a pair of on-ramp and off-ramp designed within a short distance will reduce such capacity. The results also provide that the weaving section length and headway are more sensitive for the on-off-ramp than for the off-on-ramp scenario for the curb bus lane.