An Empirical and Theoretical Study of Freeway Weave Bottlenecks

Though there have been numerous studies of freeway weaving sections (i.e., segments in which an on-ramp is followed by an off-ramp), there remains a significant lack of empirical and theoretical understanding of the traffic behavior that causes weaving sections to become bottlenecks with varying discharge flows. The present research entails empirical analysis and theoretical modeling of what triggered the bottleneck activations and discharge flow changes in two freeway weaving sections. Both sites were recurrent bottlenecks during the rush, and investigations revealed that changes in the spatial patterns of vehicular lane-changes, especially among Freeway-to-Ramp (F-R) maneuvers, caused variations in bottleneck discharge flow. When the F-R maneuvers were concentrated near a weaving section’s on-ramp, they became more disruptive, resulting in bottleneck activations with diminished discharge flows. Findings further indicated that the spatial distributions of these lane changes, in turn, were dictated by the traffic conditions in the auxiliary lane (i.e., the lane connecting the off-ramp to the upstream on-ramp). Reductions in on-ramp flows increased the attractiveness of the auxiliary lane, thus motivating F-R drivers to perform their maneuvers nearer the onramp. Conversely, increases in on-ramp flows motivated F-R drivers to perform their maneuvers over a wider stretch of the weaving section.