Dynamic Sight-distance Calculation And Safety Research Based On The Three-dimensional Alignment Of Highway Space

With the gradual conversion of highway alignment design from two-dimensional to threedimensional,relevant indicators and technical methods for highway safety evaluation also need to be studied in a three-dimensional road environment.Sight distance is an important indicator in the road design and evaluation stage,and it is an important bridge connecting road design and driving behavior.However,sight-distance is often insufficient in sharp curves in mountainous areas.At present,the calculation of sight-distance mainly adopts the twodimensional method of horizontal lateral clear distance,which is compared with the sight distance value in the specification.This method ignores the three-dimensional spatial characteristics of road alignment.Therefore,this paper takes secondary roads as an example to study the geometric description of highway alignment and three-dimensional dynamic sightdistanca calculation and analysis,analyze its application in road safety evaluation,and apply this theoretical method to actual engineering.This paper calculates the 3D dynamic sight-distance based on the geometric description of the space alignment,considers the relationship between the position and posture of the vehicle in the process of space movement,and combines the Euler transformation matrix to establish the three-dimensional alignment mathematical expression of the highway with the horizontal azimuth function and the vertical angle function as parameters.On this basis,considering the influence of the horizontal and vertical alignment,the driver’s apparent height,the height of the target obstacle,the lateral distance and the boundary constraints on the three-dimensional observable sight-distance,which is jointly constructed by the road view equation and the slope view equation Solve the model,give the minimum sight-distance solution equation of the unfavorable combination line shape,and put forward a sight-distance safety evaluation method based on the safe car-following theory.Finally,taking a secondary road in the mountainous area of Guizhou as an example,through the Matlab editing program,the safety analysis of the continuous coordination of the space curvature,torsion,three-dimensional sight-distance t and the maximum allowable initial speed along the test section is carried out.Through the safety inspection of the forward and reverse sight distance and the maximum allowable initial speed,it was found that the sight-distance was insufficient in 13 places for meeting sight-distance and4 at parking sight-distance,11 places were discontinuous sight-distance,and the maximum allowable initial speed deviated at 2 places.The analysis found that the continuity of the curvature of the highway space curve needs to ensure the continuity of the first derivative of the α and β parameters.Near the pile number of the connection point of the transition curve and the straight line,the torsion of the transition curve and the vertical curve combination section changes by orders of magnitude,and the curve is severely distorted.It will affect the driving comfort of the driver and the continuity of the sight distance;when the design speed of the secondary road is 60km/h and 80km/h,the maximum allowable initial speed is less than the design speed when the general minimum radius of the circle is adopted;the research shows that the circle at different design speeds The relationship between the radius of the curve and the lateral distance inside the lane line provides a reference for parameter selection under difficult terrain conditions;both the radius of the horizontal curve and the radius of the vertical curve have a critical point,and the critical point of the vertical curve is related to the driver’s line of sight height at the observation point The critical point of the horizontal curve is related to the radius of the vertical curve.When the radius exceeds the critical point,the value of the two-dimensional sight-distance is less than the calculated value of the three-dimensional sight-distance.The use of the two-dimensional horizontal clear distance formula for the evaluation of the sight-distance poses a safety risk.