Modeling and PARAMICS Based Evaluation of New Local Freeway Ramp-Metering Strategy that Takes Ramp Queues into Account

One of the major criticisms of ramp-metering has been the delay caused on the ramps because of the queues created by ramp control strategies. However, recently, several researchers proposed strategies that explicitly take into account ramp queues when determining metering rates. In this paper, an isolated “feedback” based ramp-metering strategy using modeling is presented. In addition to the regulation of ramp input from the freeway, the strategy calls for regulation of ramp queues by explicitly incorporating them into the model. This isolated ramp-metering strategy (Mixed Control) is tested using PARAMICS, a microscopic traffic simulation package, on a calibrated test network located in Hayward, California. In addition to Mixed Control, two other ramp control strategies, namely ALINEA (Papageorgiou et al., 1991), and New Control (Kachroo and Ozbay, 2003) are implemented in PARAMICS. Because the focus of this paper is on the evaluation of the isolated ramp control strategies, change in demand caused by ramp-metering is not considered. For this isolated ramp-metering evaluation study, we defined the system as the “upstream, downstream, and ramp” links around the metered ramp (Figure 1). The performances of three ramp control strategies are compared for two freeway demand patterns (congested and fairly congested). Based on the simulation results, all the freeway ramp control strategies tested in this paper were found to be quite effective in optimizing freeway traffic conditions (reduction in mean congestion duration on the freeway downstream link, mean downstream occupancy, and travel time (upstream and downstream links)). However, Mixed Control produced the best system (upstream, downstream and ramp links) results by achieving optimal flow on the highway while keeping the queue length on the ramp small enough to prevent spillover onto the arterial network. TRB 2004 Annual Meeting CD-ROM Paper revised from original submittal.