NCHRP 3-87 Proactive Ramp Management Under the Threat of Freeway Flow Breakdown

Contracting Agency: National Cooperative Highway Research Program

PI: Lily Elefteriadou, Ph.D.

Subcontractors: University of Bochum, Germany (Walter Brilon, Ph.D.), Telvent (Mr. Les Jacobson), Fred Hall, Ph.D., Bhagwant Persaud, 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, is to develop procedures for selecting ramp-management strategies for a freeway section under the threat of flow breakdown.  These procedures will be evaluated using simulation in conjunction with field data.  The research will be 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. 

The research team is now working on the second phase of the research project. In Task 7 the data collection plan is currently being executed as approved by the project panel and NCHRP.  Task 8 will involve the development of the real-time breakdown prediction model, as well as the assessment of the models performance under real-world conditions.  This task will also document the calibration procedures required in implementing the model at a particular site.  In Task 9 the research team will develop 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 will quantify the effectiveness of the Task 9 procedures using microscopic simulation modeling based on real-world sites, and will compare the performance of the recommended strategies to other traditional ramp management strategies.  The evaluation will consider the stochastic nature of breakdown occurrence, both in the selection of an appropriate simulator, and in the analysis.  A final report will be prepared and submitted to NCHRP in Task 11.  This report will document the entire research effort and will include as a stand-alone document the description of the breakdown prediction model so that agencies can directly apply it in their systems.