| Harmful alignment combination poses a serious threat to highway safety.The highway alignment obtained by traditionally horizontal and vertical design method exhibits continuous degradation phenomenon in Euclidean three-dimensional space,indicating different degrees of leap mutation of curvature and torsion.The continuous degradation in sapce reduces the safety of highway alignment,which is correlated with the accident rate statistically.Therefore,based on the the essence that the highway alignment is three-dimensional space curves,the research analyzed the continuous degradation indicators and accident analysis model more suitable for highway safety analysis in three-dimensional space.The research methods and results are as follows:(1)Based on some actual high-grade highways in Guangdong Province in operation,the research collected the data of highway alignment design,data of accidants on over the years and traffic volume corresponding yeas for comprehensive analysis.After pretreatment of the accident data,according to the time required for safe operation and operating range of a car in3 seconds closed to 100 meters,the research proposed a method of dividing the unit with a length of 100 meters as available segment unit.Meantime,after eliminating segments with special areas including interchanges and tunnels,available segment unit sets were sort out,and the samples that can be used for modeling were abtained.(2)Based on Frenet architecture,the calculation formula of curvature and torsion in three-dimensional space was analyzed,and the parameters in the formula were defined definitely.With the help of Python programming,the software calculating curvature and torsion was developed.The calculation process of the curvature and torsion in the three-dimensional space was completed by computer programming,which simplified the calculation.Considering the interactive influence of the segment unit alignment,the research proposed the indicators of continuous degradation can be used in traffic accident analysis model,including TCD,TTD,AC,AT,ACD and ATD.What more,collinearity of six variables was checked,and it is found that AT and ATD were collinear.(3)Considering the continuous limited nature of the dependent variable annual accident rate,Tobit regression model was used to screen indicators,and TCD,AC and ACD were determined,which had significant influence on the annual accident rate and could be used to construct the accident analysis model.Further,finite mixture Tobit regression model was proposed,and it was found that the finite mixed Tobit regression model was more suitable for the analysis,so the corresponding model expression was given.The critical risk limits of significant impact indicators were given by nonparametric estimation and survival analysis,and the evaluation standard of driving safety based on the three-dimensional alignment continuous degradation index was proposed.Finally,the results of this research are verified by the alignment optimization design and analysis of an engineering example.From the perspective of Euclidean three-dimensional space,the research studied the correlation between continuous degradation and accidents based on the concept of continuous degradation of highway alignment in three-dimensional space,which provided a certain reference for safety analysis and optimization of highway alignment design. |
