Study On The Determing Method Of Reasonable Speed Limits On Expressway Mainstream

Expressway is a vital component part of road network. It has been an important research topic for the social sectors, especially for transport sectors, about how to make freeways high efficiency, safety and comfort. There are many random and uncontrolled factors influencing the value of speed limits, like traffic volume, traffic composition, road alignment and meteorological conditions. Therefore it’s hard to find an accurate mathematical model to determine the speed limits. To solve above problems, this paper tried to analysis the affecting factors about speed limits in detail. Combined analysis result, this paper tried to using intelligent algorithms to build an appropriate method of achieving speed limits on expressway.Combined vehicle performance, safety and comfort factors, this paper chooses moderate performance vehicle as the research object, guaranteed the accident mortality and comfort in the allowable range, used the mathematical methods of choosing the smallest in the large to achieve the reference value. Through detailed analysis, the result reveals that the main influence factors are traffic volume and traffic composition, road alignment, visibility and road surface friction coefficient. Thus, use the AASHTO parking sight distance model to describe the visibility and road surface friction coefficient influence factor, which can illustrate the relationship between visibility and road surface friction coefficient and speed.According to the influence degree of influence factors, the existing research directly amended the reference value, neglecting the mutual interference between influence factors, which lead to speed limits becomes smaller. Combining the advantages of fuzzy logic algorithm and neural network algorithm, this paper proposes the RBF fuzzy neural network algorithm. To adjust the corrected value of influence factors reasonably, use the corrected value which adjusted to correct the reference value, finally the speed limits on expressway mainstream is get. The fuzzy logic, RBF neural network, the RBF fuzzy neural network intelligent algorithms are used to study on determing method of speed limits on expressway mainstream. The simulation results show that, the proposed algorithm is effective and demonstrated the advantages of the fuzzy logic algorithm and neural network algorithm, thus indicated its feasibility.Intelligent algorithms are applied to study on determing method of speed limits on expressway mainstream, so that the design of speed controller does not depend on the mathematical model of the controlled object, and thus enhanced the robustness. Because this method can effectively increase the capacity of expressway, reduce travel time, and reduce the occurrence of accidents, and at the same time reduce the driver’s driving strength, it proved a great practical value.