Research On Operating Speed Of Two-Lane Highways Based On Environment

With the rapid development of highway construction and the degree of the improvement of mobility, although traffic brings an efficient and convenient for people, economic and comfort at the same time, its security has increasingly become a hot social issue. In the system consist of human, vehicle and road, poor road conditions is one of the important causes of traffic accidents. The current concept of routh design conserns the safety of a single section, but often neglects the safety of adjacent sections, namely, the operating speed of the adjacent sections of coordination. In order to guide future road design and safety evaluation, it is necessary to further expand the theory of the operating speed. Therefore, to lucubrate the relate theory of operating speed of two-lane highway, composition of more than 75% of all highway, will help to improve desigh theory of operating speed , which has important theoretical significance and application to our future road construction and management.Two-lane highway has diverse cross-section, and the design indicators are more flexible, the road environment along the road is also more complex. To create models of operating speed with simple line indicator seems uncomprehensive. Therefore, the models of operating speed must be a comprehensive analysis of various factors, and based on these the models of operating speed of two-lane highway can be built .Experiments had been performed to analyze the change of continuous speed of the cars for experiments and study the change of the time headway and the fluctuation rules of the speed differentiae. Then time headway was regarded as the measurement index of free-flow, and time headway of free-flow should be taken more than 9 s interval. In dry and wet conditions, operating speed is not very different in the statistical sense, and it is unnecessary to limit the wet and dry conditions. By analyzing the value of the speed deviation and the statistical distribution of values,it is reasonable to selecte the 85 percentile of the cumulative speed distribution curve as operating speed. On this basis, the impacts of the various factors on operating speed are analyzed. Conclusion is made that the operating speed is determined by the combined effects of the road alignment and the road environment.Operating speed of two-lane highway should first establish a basic model, and then build modified model based on the road environments.Bisic speed model is entirely determined by road geometry.Two-lane highway section is divided into units as tangent sections, horizontal curves, veticle curves,and combination of horizontal and vertical,based on the index of geometry linetype. Operating speed of tangent sections depends on line length, the adjacent horizontal curve radius and the driver's expectations. Experiments were drawn to study the acceleration and deceleration characteristics of vehicles, and the model of the acceleration and deceleration of tangents was built.Based on these, the model of the tangents was built between operating speed and initial speed, regional categories and the length. Section of horizontal curve speed depends on the horizontal curve radius, the length of horizontal curve and initial velocity.Large amounts of data were surveyed establish a horizontal curve section of the operating speed model, using statistical regression. According to kinetic theory, the speed of longitudinal section has close relation with dynamic performance of the vehicle.And the relation of the speed and the initial speed is analyzed and the model of the operating speed of longitudinal sections is built. Operating speed of combination of horizontal and vertical sections relates to initial speed, horizontal curve radius, the slope difference,and the model of operating speed is built bases on large amounts of data.Road environment two-lane highway can be divided into two categories, one is random factors,which can be called the road side interference, including the shoulder parking, shoulder pedestrians, non-motor vehicles, and the other is the inherent property of the road, including the sight distance, road-side clearance, and accesses of the road.The trend stable speed of the vehicle's in the different visibility (corresponding to line of sight) is studied in driving simulator, and the the impact of sight distance on operating speed is analysed. The theoretical model between sight distance and operating speed is built, and then the mode of sections with limited sight distance is built through the field data using stepwise regression method. For different roadside clearance, through field data investigation and analysis, roadside clearance and operating speed show a logarithmic relation and then obtain the correction factor of roadside clearance on the basic model. When drivers travel on the streets of the road, the first is expected to have an insecure, that the streets of traffic on the section is not safe, so even if there is no line of sight of insecurity, the driver will choose to slow down. The behavior of their choice lies on both sides of the space and the size of the road. Through targeted investigation and analysis, the model of operating speed of streetlized highway is built. Mostly two-lane highway access is an important feature. Through delay investigation, the paper studied the relation between the access density and operating speed, and the the relevant model is built. The impact of roadside interference relate to the number of interfering factors, category, and horizontal spacing.The article studied the ampact of different types of roadside interference on the speed of the vehicle, and built the interference factor model by theoretical analysis of the horizontal distance and objects integrated arrival rate.By analyzing the mechanism of the accident ,the accident was triggered by the sudden change of the traffic system, and the route should be designed to be indicators of changes in the amenity and comfort, try to avoid sudden changes in the design elements. Then experiments were drawn to study the relations among the driver's heart rate variability and work load degree and operating speed, and the indicators as consistency of design speed, operating speed coordination, speed and acceleration of lower coefficient and velocity gradient were studied to find the relation between safety and above indicators.The conclusion obtained that the road safety indicators should choosed as operating speed coordination and velocity gradient.Speed coordination evaluation criteria: |△V 85 |≤10km / h, good coordination; |△V85| for the 10-20km / h: common coordination, when conditions permited adjacent sections of technical indicators should be adjusted, so that the speed differentiate is less than or equal to 10km / h; |△V85 |≥20km / h: poor coordination speed, need to re-adjust the design of the adjacent sections. Velocity gradient evaluation criteria:Gv≤0.10, good road safety; 0.10≤Gv <0.15, common road safety; Gv > 0.15, poor road safety, the adjacent sections need to re-adjust. On this basis, the paper proposed two-lane highway safety audit of routes, providing theoretical support for the route design and the future speed management.