Urban Highway Variable Speed Limit Strategy Research

Variable speed control, which is system to limit the speed of the main road through setting up sensor of traffic information, sensor of weather information, and variable speed limits signal and other electronic facilities on the freeway and urban expressway, so that the vehicle speed change can be followed to the traffic flow density on the main road, and make certain the uniformity and stability of the main road traffic flow, and improve the service level of main roads. Variable speed limit system as a subsystem of ITS, although has been a certain amount of use in the freeway system, and has achieved good social and economic benefits, but study on variable speed limit control on the urban expressway is few. Available study on variable speed limit is mostly using the traffic volume as a control variable and control strategy is relatively simple. Meanwhile these studies were not on the combination of ramp control strategy of variable speed limit. Therefore, how to coordinate use of main road and ramp control, depending on different road, traffic, weather conditions to formulate control strategies to ensure high efficiency, security, economy and comfort of operation of expressway system, is my purposes to study on variable speed limit control strategy for urban expressway.Based on the purpose of my study, the main work and research result are in the following areas:First, summarize the concept, function and control methods and strategies of variable speed limit system, and conclude the status of variable speed limit system implementation at home and abroad; the definition, characteristics and classification of urban expressway were summarized;Secondly, collect speed, flow data on the urban expressway in the city of Kunming and Shanghai, respectively, study on the characteristics of the speed of main road, on-ramp and off-ramp, diverging point and confluence point of the expressway, so that get the basic characteristics of these types of speed and the velocity distribution; study on the main road speed-volume relationship and found that the speed characteristics of different flow range and features of the distribution are different; study on the main road speed-density relationship, using the speed-density relations of Markos Papageorgiou macroscopic dynamic traffic flow model and found that this were fitted to the measured data;Again, according to the basic principles of variable speed control, put forward that using different control strategies under different traffic flow density; use the macroscopic dynamic traffic flow model to establish a variable speed limit model, while setup the parameters of the model; using the integral regulator to establish a on-ramp control model; presented four objective function of the variable speed limit, namely road service volume, travel time, average waiting time of off-ramp and travel delay time; using the combination of four objective function to set up optimization problems of the system under the three different density states of low, medium and high; partly considering three factors of off-ramp, adverse weather and road linear, to establish three speed constraints of the main road based on security;Finally, using the simulation software VISSIM to establish a model of basic sections of expressway with the on-ramp and off-ramp, so the variable speed limit strategy is simulated. Through contrasting the data of same objective function under the state with and without control, it is observed that studies on the variable speed limit strategy in this paper are effective;...