A Study on the variable freeway speed-limit control strategy
Date Issued
2010
Date
2010
Author(s)
Lu, Yan-Cong
Abstract
In the main stream of freeway, the non-homogenous traffic flow is the main reason of congestion or congestion expansion. When the flow is closed to the road capacity, the small disturbance in the platoon will affect the traffic flow smooth run, and cause the shock wave, and then it influences the downstream traffic. Finally it results in the expansion of the congestion. Therefore, if there is the properly speed limit control tragedy to recommend the drivers to drive in the appropriate speed, in order to let the traffic flow reduce the occurrence of instability situation and ease the shock effect in order to achieve smooth traffic flow. Thus, it is essential to develop a dynamic optimal speed-limit control model which can maximize the traffic efficiency.
Based on this, this study proposes a macroscopic traffic models and continuity model-based model for dynamic variable speed-limit control under the congestion conditions caused by the bottleneck. The objective is maximizing the total throughput in the control boundary, and there are five parameters in the mathematical model which need to be calibrated by using field data: (1) the free velocity, (2) the jam density, (3) the parameter of the relationship between density and speed over time, (4) the parameter of the shock wave over time, (5) the downstream boundary flow of bottleneck.
The freeway No.5 is the research object of this study. Firstly, the study uses the field data to establish the simulation of the northern section of Freeway No.5, in order to reproduce the congestion, for this, this study analyzes the characteristics of bottleneck section of the road, and finds the detail reason of the Hsuehshan Tunnel congestion is the exhibition of land changing, speed limit changes and increase of the safety headway parameters. And this study find out the model calibrated parameters , the car-following factor which is needed by the simulation and the component of the control, which includes the speed limit sign and detector location, and the speed limit value, control boundary selection.
This study put the variable speed limit control into the simulation network, and the total throughput increased by 19.5%, average travel time decreased by 8.44%, etc. It shows that this model can indeed improve the performance of the network in the Freeway No.5. With the increasing of the flow, although the performance improvement is reduced, but it still has the effect on the main stream. The result indicates that the model of this paper is effective on the simulation network.
Subjects
Variable Speed Limit
Traffic Control
Freeway
Traffic Simulation
SDGs
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