| In recent years,with the continuous expansion of the scale of my country’s modern city construction,the city’s demand for transportation has been on a rapid upward trend.Speed limits on urban expressways focus on the urban backbone road network,and are committed to quickly evacuate a large amount of traffic within the city and relieve inbound traffic on highways around the city,so as to achieve the purpose of active traffic control and truly improve the urban traffic travel experience.Due to various reasons such as time period,accidents,construction,etc.,the traffic conditions of expressways are a dynamic process,and driving safety and traffic efficiency cannot be guaranteed.This article first analyzes the distribution characteristics of traffic flow and vehicle types on the main roads of urban expressways through field investigations,and analyzes the temporal and spatial distribution characteristics of different road operating speeds under the existing speed limit schemes,from the speed dispersion,the speed limit and the coordination of the operating speed Analyze the problems of the main road speed limit in terms of driving safety and traffic efficiency.Secondly,analyze the safety status of expressway main roads through time to collision(TTC),analyze the benefit status through travel time,travel delays,and the number of stops,and combine the correlation between traffic safety,benefits and speed limit to obtain the basis for speed limit optimization.Then design a VISSIM simulation experiment to explore the mechanism of the impact of speed limit on traffic safety and benefits.In terms of traffic safety,it is found that the average improvement effect of speed limit on vehicle speed dispersion is 26.1%,which increases the average headway time by 7.3%,effectively reducing it.Road accident risk,and the smaller the speed limit value,the lower the accident risk;in terms of traffic efficiency,the speed limit can be found to smooth traffic flow,the increase rate of blockage density is 10%,the maximum free flow capacity increase rate is 13.6%,and the delay The time is reduced by about40%.Then build a speed limit optimization model from two aspects of driving safety and traffic efficiency: use traffic flow as a variable of the speed limit model to formulate the setting method for the speed limit of the whole line and the local speed limit of the bottleneck section;carry out the dynamic traffic flow safety model according to TTC=2s Optimize,construct a safe speed limit model based on TTC,construct a benefit speed limit model based on the theory of continuous traffic flow according to the shortest travel time and maximize the capacity,propose a safety and benefit control function,and find it through the improved Euclidean distance The optimal solution for the speed limit value.Using VISSIM simulation experiments,the optimal speed limit plan was compared and analyzed with the speed limit plans of 80km/h and 100km/h on the whole line.The results found that when there is no traffic bottleneck in the express section,the advantage of the optimal speed limit is not obvious,but In certain high-density sections or local lanes where service is suspended and traffic congestion occurs,the advantages of speed limit for traffic safety and efficiency optimization are even more prominent.Finally,aiming at the speed limit method on the main road of expressways and the arrangement of the existing speed limit signs,an optimization method for the reasonable arrangement of speed limit signs is proposed.This method is based on the accident risk prediction model to identify the dangerous sections of the main road of the expressway.Then,according to the different speed limit schemes and the location and quantity of speed limit signs,each scheme is evaluated,and the investment-benefit analysis is carried out to determine the most Excellent logo layout plan. |
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