Coordinated Freeway Ramp Metering Control Model
Date Issued
2010
Date
2010
Author(s)
Cheng, Kai-Yu
Abstract
The freeway always occurrs critical congestion on vacations in Taiwan, and ramp metering control is one of the ways to solve the congestion problem of freeway. All ramp metering on freeway at present are controlled isolated and the metering adopted fixed time class which can not detected real-time flow of mainline and ramp, and it will lead the queue of mainline back up onto upstream when a ramp with excess demand; at this time, it must adjust the metering rates of ramps at upstream, so in this research, the network was considered, and the coordinated ramp metering control model which formulated as linear optimal control model and the metering rate executed with traffic-responsive control was proposed.
This optimal control model was formulated by using modified cell transmission model (MCTM), it easily to calculate, and it can apply to dynamic control with the basic rules of MCTM. The framework of this research divided into two steps. The first step was to calibrate the MCTM parameters, and to ensure MCTM can replicate the freeway traffic behaviors; the second step was to calculate the optimal metering rates, and then evaluate its performances.
In this research, the optimal model was tested numerically using data from a severely congested stretch of freeway at National Freeway No.5 during 2009/5/28 to 2009/5/31, and it were also used to calibrate MCTM parameters. Then, the Mean Absolute Percentage Error (MAPE) was selected as evaluation index, and the results showed that the MAPE of the MCTM falls into a reasonable range.
There are two conditions when the metering was calculated, the first one is the optimal control model without the consideration of the onramp queue length constrain, and the second one is the optimal control model which consider the onramp queue length constrain. In addition, total time spent (TTS), total travel time (TTT) and total waiting time (TWT) were used to evaluation performances of the two conditions. The results showed that the proposed model can improve the congestion problems of National Freeway No.5 in both situations. However, the first condition causes long queue length at Toucheng onramp, thus the second condition is regarded as the better strategy.
Subjects
Ramp Metering Control
Traffic-Responsive Control
Optimal Control
Traffic Flow Model
Cell Transmission Model
Type
thesis
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