Research On The Influence Of Posted Speed Limit On The Quality Of Expressway Traffic Flow

As an important part of expressway operation management,posted speed limit directly affects many aspects such as traffic safety,carbon emissions,vehicle traffic efficiency and overall operation quality of traffic flow.Compared with traffic safety,transportation management departments and scientific researchers do not pay enough attention to the impact of speed limits on the overall operation quality of traffic flow,targeted research is lacking and the theory is weak.As a result,there are many controversies about the concept and connotation of operation quality,and it is impossible to clarify the degree or law of the influence of speed limits on the operation quality of traffic flow.Based on this,on the basis of clarifying the concept and connotation of traffic quality,this paper focuses on the impact of speed limit on the quality of traffic flow operation.It provides a theoretical basis for formulating a reasonable speed limit scheme.Based on the analysis of domestic and foreign literature,the connotation and existing problems of the main concepts characterizing the operation characteristics of traffic flow are discussed.On the basis of extensive research and interviews,etc.,vehicle speed dispersion and traffic efficiency were defined as the indicators of traffic quality.In order to explore the influence of speed limit on vehicle velocity dispersion,this paper adopts the method of field test to collect the traffic flow velocity data of three different speed limit value sections,including the vehicle velocity in the state of free flow and non-free flow.Origin and SPSS software were used for the discrete analysis of speed,and the speed distribution,percentile speed,standard deviation and coefficient of variation were obtained under different speed limit values.The results show that the standard deviation of vehicle speed,the coefficient of variation and the characteristic speed difference all increase with the increase of the limiting speed under the condition of free flow,which indicates that the higher the limiting speed value is,the more serious the dispersion of vehicle speed is.In the non-free flow state,the speed limit is no longer the main factor affecting the dispersion of the speed of the traffic flow vehicles.The speed of the traffic flow is mainly affected by the density of the traffic flow.On the basis of summarizing the development process of traffic efficiency,the internationally popular traffic efficiency calculation method is introduced,and the Origin and SPSS software are used to calculate the traffic efficiency of the measured data under ideal conditions and under different speed limits respectively.The research shows that,in the state of free flow,the influence of restricted speed on traffic efficiency is significant,which is mainly manifested in that the higher the restricted speed is,the greater the improvement of the overall average speed of traffic flow is.In the state of non-free flow,the influence of restricted speed on traffic efficiency is limited,and the greater the traffic flow density is,the smaller the influence of restricted speed on traffic flow efficiency is.The research results can provide reference for the formulation of speed limit scheme and play a positive role in improving the road traffic quality.