Mechanism of a Freeway Weaving Section as Typical Traffic Bottleneck

This paper presents an empirical study of freeway weave bottleneck to understand the weave’s capacity-change mechanism in detail and proposes a basic structure for weaving capacity modelling. To these ends, a weave bottleneck in central Bangkok was selected and videotaped for two morning’s rush hours. The data were then manually extracted and analyzed by using oblique-coordinate based plots to reveal unprecedented traffic characteristics at the weaving section. These data verify that the capacity of this weaving bottleneck is not fixed and fluctuates over time depending on the on-ramp and off-ramp flows. It was found that on-ramp surges induce lane changes from slow to fast lanes, and cause an increase in the overall freeway capacity. On the other hand, any off-ramp surges influence lane changes from fast to slow lanes, bringing the overall freeway capacity down. Furthermore, a basic structure for modelling the capacity at a weaving bottleneck is proposed according to the mechanism found herein.