Probability of Capacity Enhancement and Disruption for Freeway Ramp Controls analysis by Gap-acceptance and Queuing Models

Transportation Research Record: Journal of the Transportation Research Board, No. 2278, Transportation Research Board of the National Academies, Washington, D.C., 2012, pp. 1–12. DOI: 10.3141/2278-01 Z. Z. Tian, Department of Civil and Environmental Engineering, University of Nevada, Reno, MS 0258, Reno, NV 89557. N. Wu, Institute for Traffic Engineering, Ruhr University Bochum, 44801 Bochum, Germany. Corresponding author: N. Wu, [email protected]. freeway traffic flow rate reaches a certain threshold level. When freeway traffic is low, there will be enough gaps in the freeway flow to accommodate the ramp flow, even when ramp traffic enters the freeway in platoons. In practice, ramp metering threshold values are typically determined on the basis of empirical studies. This paper develops a new theoretical model based on gap-acceptance and queuing theory that addresses the impacts of the three types of ramp control and traffic arrival patterns; the model can be used to determine ramp metering threshold values. Figure 1 shows some of the merging situations in which the ramp traffic can be accommodated without significant disruption to the main-line traffic. These situations involve no more than one vehicle making a lane change or slowing down, which is defined as no disruption events later in this paper. The traffic flow rates on the freeway main line and the ramp that would result in no disruption of freeway operations are defined as the flow thresholds for ramp metering. Traffic flow rates below the threshold values are not necessary for initiating ramp metering operations because normal freeway operations would maintain. Models based on gap-acceptance to determine the flow threshold values are presented in the following sections of this paper.