An Optimization Model of Coordinated VSL and Ramp Metering Control on Freeway

With the growth of private car holding rate and usage rate, traffic volume increases rapidly, huge scope and long-time congestion happens in the peak hour or on long vacations on freeway, the congestion also blocked back to local roads which cause entirely congestion. The efficient of freeway reduced and social cost increased due to congestion, in order to raise the efficient and reduce social cost, it is necessary to adopt relative traffic control strategy to maintain the stability of traffic flow.
The research takes north bound of freeway No. 5 as an example. First of all, to analysis the congestion characteristics in the research scope by the data from vehicle detector. It is known that the congestion segment is focused on HsuehShan tunnel, and car velocity reduced from 90km/hr to 10km/hr in 5 minutes, which is the catastrophe phenomena. As a result, this research construct a optimal model of coordinated VSL(Variable Speed Limit) and ramp metering by mathematical program, to control traffic flow entering HsuehShan tunnel with gradually speed reduction by the characteristic of VSL, also coordinate with upstream ramp interlocked control, to mitigate or even prevent from the congestion of HsuehShan tunnel. This model also based on discrete second order macroscope traffic flow model - METANET to develop a macroscope traffic flow model witch fits the north bound segment of freeway No. 5, which is named "METANET long tunnel model" by this research.
However, due to the difficulty of parameter calibration and slow solving rate of optimal model, it is unrealistic to be used in online control. In order to overcome this difficulty, Artificial neural network is used to construct the prediction model and predict the input parameters of optimal model, also heuristic algorithm is used to enhance the solving rate, with the combination to reach the goal of online control.
In order to assess the performance of this model, microscope simulation software - VISSIM is used to sketch the network of the northbound of freeway No. 5, the validation process is taken to confirm the reality of simulation network. Finally, the plug-in software VisVap is been used to apply the result optimal model into simulation model. The result indicated that the mainline travel time and total throughput of HsuehShan tunnel increased significantly after control, which indicate the usage rate of northbound of freeway No. 5 is enhanced effectively by the control model in this research.