Zhang, Lei and David Levinson (2010). Ramp Metering and Freeway Bottleneck Capacity.
This study aims to determine whether ramp meters increase the capacity of active freeway bottlenecks. The traffic flow characteristics at 27 active bottlenecks in the Twin Cities have been studied for seven weeks without ramp metering and seven weeks with ramp metering. A methodology for systematically identifying active freeway bottlenecks in a metropolitan area is proposed, which relies on two occupancy threshold values and is compared to an established diagnostic method - transformed cumulative count curves. A series of hypotheses regarding the relationships between ramp metering and the capacity of active bottlenecks are developed and tested against empirical traffic data. It is found that meters increase the bottleneck capacity by postponing and sometimes eliminating bottleneck activations, accommodating higher flows during the pre-queue transition period, and increasing queue discharge flow rates after breakdown. Results also suggest that flow drops after breakdown and the percentage flow drops at various bottlenecks follow a normal distribution. The implications of these findings on the design of efficient ramp control strategies, as well as future research directions, are discussed.
(pre-print available here.
(For those of you who give up hope after rejection, this paper was first submitted in 2003! My co-author earned an MS, another MS, a Ph.D. and has held two faculty positions over the duration of this article. I myself have had 3 children. After various recommendations for revise and resubmit, and changes of editor, it was lost twice by the (previous) editor of TRa (prior to the electronic submission system, which at least removes one excuse from the editor's arsenal), and had been accepted before it was lost so had to go through re-review after the change in editorship. I think it is quite interesting and the analysis and results hold up, and so I encourage you to read it and cite it if it is relevant to your work. The final review process was relatively fast, taking 17 months from resubmission to print. And only 13 months from resubmission to online.)