Abstract
ABSTRACTIn freeways, the capacity drop means that the maximum traffic flow is higher than congestion discharge rates there. Various capacity drop magnitudes have been empirically observed before. But the mechanism behind this wide capacity drop range is not yet found. This contribution fills in the gap by relating the congestion discharge rates to different congestions in empirical observations. Two days’ data show that the outflows of stop-and-go waves are always lower than those of standing queues. Different discharge rates, ranging from 5220 to 6040 veh/h at the same site, always accompany different congestion states. Moreover, the different observations show that a higher discharge rate means a higher density in the free-flow branch in the fundamental diagram. This contribution shows that discharging rates probably could be controlled by transforming the congestion states. For instance, transforming a stop-and-go wave into a standing queue at a bottleneck might increase the bottleneck throughput.
Highlights
Congestion is observed as a form of vehicular queueing, which can be categorized into stopand-go waves and standing queues
Previous research (Laval and Daganzo 2006; Chung, Rudjanakanoknad, and Cassidy 2007) shows that the capacity drop is strongly related to the congestion level; it is expected that downstream of a stop-and-go wave traffic states differ from those downstream of a standing queue
By comparing the outflows downstream of congestion, this paper shows the capacity drop corresponding to the two different congestion types, stop-and-go wave and standing queue
Summary
Congestion is observed as a form of vehicular queueing, which can be categorized into stopand-go waves and standing queues. Most of previous researches observe the capacity drop phenomenon at active bottlenecks Few of those studies reveal features of capacity drop downstream of a stop-and-go wave. Previous research shows that discharging flows of standing queues at one bottleneck only exhibit small deviations (Cassidy and Bertini 1999). The study of the flow distribution can show the utilization of lanes when the capacity drop is observed, which can benefit increasing queue discharge rates with multi-lane dynamic management. To answer those questions, this paper studies a traffic scenario where a standing queue forms immediately after a stop-and-go wave passes.
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