NCHRP 3-87 Proactive Ramp Management Under the Threat of Freeway Flow Breakdown
Contracting Agency: National Cooperative Highway Research Program Subcontractors: University of Bochum, Germany (Walter Brilon, Ph.D.), Telvent (Mr. Les Jacobson), Fred Hall, Ph.D., Bhagwant Persaud, Ph.D. Principal Investigator: Lily Elefteriadou, Ph.D.
As congestion continues to increase, many agencies have considered alternative methods and advanced technology to make better use of existing capacity. These methods and technology are often integrated into freeway management programs that seek to manage, operate, and maintain freeway facilities in an efficient and cost-effective manner (Ramp Management and Control Handbook - RMCH, 2005). Ramp management is one of several functions performed on a daily basis to maximize the use of existing capacity.
The objective of this project, which started in October 2006, was to develop procedures for selecting ramp-management strategies for a freeway section under the threat of flow breakdown. These procedures were evaluated using simulation in conjunction with field data. The research was conducted in eleven tasks. Task 1 reviewed and summarized research findings to identify factors that affect freeway capacity, review and describe previous data collection efforts and models that have been developed for the prediction of breakdown, and review any documented effects of ramp management strategies on the onset of breakdown. In Task 2, the research team developed a working definition of freeway-flow breakdown, discussed typical flow-breakdown causes and described the process of breakdown at common types of bottlenecks. Task 3 described ramp-management strategies that have the potential to delay or prevent freeway-flow breakdown. It also described specific characteristics of the breakdown process that could be used to enhance the effectiveness of these strategies, in delaying or preventing breakdown. Task 4 identified the functional and operational requirements of a real-time model to predict freeway-flow breakdown, and provided preliminary information for the implementation of appropriate ramp-management strategies. Task 5 prepared a data collection and analysis plan to support the development of a real-time breakdown prediction model. Task 6 produced an interim report, which detailed the work conducted in Tasks 1 through 5 along with a detailed work plan and a revised budget for the remaining tasks. Task 7 executed the data collection plan as approved by the project panel and NCHRP. Task 8 involved the development of the real-time breakdown prediction model, as well as the assessment of the models performance under real-world conditions. This task also documented the calibration procedures required in implementing the model at a particular site. In Task 9 the research team developed procedures for using the outputs of the breakdown prediction model to select ramp-management strategies to prevent or delay breakdown. In Task 10, the research team quantified the effectiveness of the Task 9 procedures using microscopic simulation modeling based on real-world sites, and compared the performance of the recommended strategies to other traditional ramp management strategies. A final report was prepared and submitted to NCHRP in Task 11. This report documented the entire research effort and included as a stand-alone document the description of the breakdown prediction model so that agencies can directly apply it in their systems.
Transportation Research Center Lily Elefteriadou, Ph.D., TRC Director
University of Florida Civil & Coastal Engineering
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