Evaluation Of Local And System-Wide Effects Of Feedback-Based Ramp Metering Strategies Using Microscopic Simulation

One of the most widely used control measures for freeway control is ramp metering. Ramp metering can be local and system-wide. Local controls consider an isolated section of the network and respond only to the changes in local conditions, whereas system-wide controls consider a series of entrance ramps and aim to coordinate the response of all the ramps in the system. The focus is to show local and system-wide effects of a new local ramp metering strategy, namely MIXCROS (Ozbay and Kachroo 2003), on a medium-size test network modeled using a microscopic simulation environment, PARAMICS, and compare its performance with another well-known control, namely ALINEA (Papageorgiou et al. 1991) These local controls are implemented on four on-ramps along the freeway corridor located in South Jersey. Local controls are shown to reasonably improve traffic conditions locally. However, some negative impacts are observed downstream of the metered ramps, mainly as a result of increased flow owing to better ramp management (Zhang and Recker 1999, Nsour et al. 1992). The location of the metered ramps influences the success of the local ramp metering implementations; increase in the number of vehicles released from upstream bottlenecks leads to congestion in the downstream locations, thereby decreasing the efficiency of the local controls. Another important result from the modeling of the two local ramp controls in this and similar studies (Zhang and Recker 1999, Gardes et al. 2001, Gardes et al. 2003, Ozbay et al. 2004) is that the impact of on-ramp queue on system-wide average travel time is very significant. However, because of its proactive nature in handling on-ramp queues, the ramp metering strategy proposed and tested in this paper, MIXCROS, increases the throughput both in the ramp systems and the rest of the network while decreasing the total average travel time of the whole system.