Ramp Metering and Freeway Bottleneck Capacity
Oregon State University
David Matthew Levinson
University of Minnesota - Twin Cities
January 20, 2009
Transportation Research Part A, Vol. 44, pp. 218-235, 2010
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.
Number of Pages in PDF File: 18
Keywords: Ramp metering, Highway capacity, Active bottleneck, Queue discharge flow, Twin Cities ramp meter shut-off
JEL Classification: R40, R41
Date posted: January 6, 2011 ; Last revised: January 22, 2011
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