Title page for ETD etd-12172010-131604

Type of Document Master's Thesis
Author El-Metwally, Maha
URN etd-12172010-131604
Title A Study of the Capacity Drop Phenomenon at Time-Dependent and Time-Independent Bottlenecks
Degree Master of Science
Department Civil Engineering
Advisory Committee
Advisor Name Title
Rakha, Hesham Ahmed Committee Chair
El-Shawarby, Ihab Committee Member
Hobeika, Antoine G. Committee Member
  • Time-dependent Bottlenecks
  • Onset of Congestion
  • Capacity Drop
  • Time-independent Bottlenecks
Date of Defense 2010-12-06
Availability unrestricted
The fact that traffic congestion upstream of a bottleneck causes a reduction in the discharge flow rate through the bottleneck has been well documented in several empirical studies. However, what has been missing is an understanding of the causes of these empirically observed flow reductions. An identification of these causes is important in order to develop various mitigation schemes through the use of emerging technology.

The concept of capacity drop can be introduced at time-independent bottlenecks (e.g. freeways) as well as time-dependent bottlenecks (e.g. signalized intersections). While to the author’s knowledge no one has attempted to link these phenomena, the research presented in this thesis serves as a first step in doing so. The research uses the INTEGRATION simulation software, after demonstrating its validity against empirical data, to simulate time-independent and time-dependent bottlenecks in an attempt to characterize and understand the contributing factors to these flow reductions.

Initially, the INTEGRATION simulation software is validated by comparing its results to empirically observed traffic stream behavior. This thesis demonstrates that the discharge flow rate is reduced at stationary bottlenecks at the onset of congestion. These reductions at stationary bottlenecks are not recovered as the traffic stream propagates downstream. Furthermore, these reductions are not impacted by the level of vehicle acceleration. Alternatively, the drop in the discharge flow rate caused by time-dependent bottleneck is recoverable and is dependent on the level of acceleration. The difference in behavior is attributed to the fact that in the case of a stationary bottleneck the delay in vehicle headways exceeds the losses caused by vehicle accelerations and thus is not recoverable. In the case of vehicles discharging from a backward recovery wave the dominant factor is the delay caused by vehicle acceleration and this can be recuperated as the traffic stream travels downstream.

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