Method for Estimating Capacity Reduction in High-Occupancy-Vehicle Lane Ingress and Egress Sections

Abstract

In high-occupancy-vehicle (HOV) facility design, there are concerns about the impacts of merging and weaving movements at the ingress and egress (I/E) sections of a barrier-separated freeway HOV lane. Weaves and merges can disturb traffic flow and cause freeway capacity reduction at HOV-lane I/E sections. Such capacity reductions can cause bottlenecks that could eventually reduce the benefit of an HOV lane. An impact analysis regarding capacity reduction is necessary, which can improve HOV-lane operations by leading to reasonable design options that minimize the capacity reduction. This study developed a method for estimating the capacity reductions at freeway HOV-lane I/E sections under various geometric and operating conditions, which is an effective tool for HOV facility planning, design, and operations analysis. The study first identified the major factors that affect freeway HOV-lane I/E section capacity. Then it explored the relationship between capacity reduction and the impact factors on the basis of a database developed from field collection and a freeway simulation model. Finally, the study developed an applicable equation for estimating capacity reduction using nonlinear regression with a third-order polynomial format. The equation was tested through a case study, the results of which indicate that the equation can yield reasonable results, satisfying the 95 percent confidence interval, in capacity reduction estimation.