Performance Analysis and Control Design for On-ramp Metering of Active Merging Bottlenecks

The complex interplay among merging, lane-changing, and accelerating behaviors plays an important role in determining the performance of a congested merging area. Especially, once a merging bottleneck is activated, the discharging flow-rate can drop by 10% (about 800 vph on a four-lane freeway); such a capacity drop can lead to excessive traffic queues and stop-and-go traffic patterns and increase fuel consumption and greenhouse gas (GHG) emissions. The objective of this research is to analyze the performance and design the control parameters for both pretimed and traffic-responsive on-ramp metering of congested merging bottlenecks. This research will: (1) quantify the congestion mitigation effects of different ramp metering algorithms at an active merging bottleneck; (2) design control parameters for efficient and robust traffic responsive ramp metering algorithms; (3) identify demand patterns when ramp metering algorithms are effective; and (4) develop a set of simple decision-support tools for ramp metering with both kinematic wave models and microscopic simulations. The research will help Caltrans to make decisions on the necessity, priority, algorithm, and parameter tuning related to ramp metering. This research will lead to a set of decision tools that can help to answer a series of questions: Is a ramp meter warranted at a location? Which merge areas should be given higher priorities given a limited budget? Should pretimed or traffic responsive metering algorithms be implemented? What kind of control parameters are the best?