| In metropolises, freeway is the skeleton of the road network and main part of urban rapid transit, which undertakes the majority of the transportation, and meets the need of development of urban transportation with the character of fast, efficient, convenient and safe. Meanwhile, with the development of city and increase of traffic demand, the phenomena of congestion in the free way is increasing rapidly, and the intrinsic "fast" character of freeway is diminishing, the main reason for which is that the congestion in off-ramp and downstream intersection is difficult to relieve. Therefore, how to improve the traffic capacity of freeway and decrease the congestion in off-ramp and downstream intersection becomes a problem urgent to be solved.At present, the research on urban freeway system mainly concentrate on the control of main road and on-ramp of freeway, while there’re little research on the off-ramp control and coordinated control between main road and auxiliary road. Therefore, the article makes research emphatically on the coordinated control among off-ramp, auxiliary road and downstream intersection, the traffic type of which is common in metropolises like Beijing, Shanghai and Guangzhou, but little research is related to that.On the other hand, the urban traffic control present a typical hybrid character, and the existing ways of modeling based on continuous system and discrete system respectively are all difficult to satisfy the demand of hybrid control, thus the innovation and investigation on the hybrid control modeling and control method need to be deepen. Therefore, the article made an in-depth research on the coordinated control among off-ramp, auxiliary road and downstream intersection by using model predictive control method, based on Mixed Logic Dynamic MLD (Mixed Logic Dynamic) modeling method.The main research contents are shown as follows:(1) Aiming at the special problem that the queue length of off-ramp needs to be short while coordinating the control among the off-ramp and downstream intersection, the article established a state equation based on the model of queue length per lane per meter, and chose the queue length of off-ramp, auxiliary road-main road intersection, and downstream intersection as continuous state variables, the switching signal of traffic light as discrete control variable. Next, the article set up a MLD model of coordinated control of off-ramp, auxiliary road and downstream junction, and the MLD model of adjacent intersections.(2) The article edited and analysised the Mixed Logic Dynamic Model by HYSDEL (Hybrid System Description Language) languse, and get HYSDEL program of the model. In matlab, model program was compiled for hybrid computing model by HYSDEL editor, and the feasibility of the model was verified.(3) The article chose signal coordinated control MLD model of adjacent intersection as study object, and made an optimized control utilizing MIQP and MILP in model predictive control respectively. The article simulated the model by MATLAB, the result shows that the control effect of MILP is better than MIQP.(4) The article chose signal coordinated control MLD model of off-ramp, auxiliary road and downstream intersection as study object, compared and investigated the effect of model predictive control with condition of with traffic signal and without traffic signal respectively. The simulation results show that the method is able to optimize the control of the MLD model.The research result of the paper has theory and engineering significance in increasing the control effect, elevating the traffic capacity, and exploring the new method of traffic control of urban freeway. |
PDF Full Text Request