Study On The Relationship Between The Vertical Geometric Alignments And Traffic Safety Of Highway

The highway vertical alignment is an important part of the highway alignment,and it has a crucial influence on the highway traffic safety.Therefore,the study of the relationship between vertical alignment and traffic safety is of great significance to improve the traffic safety level of the highway.Based on the investigation of traffic accidents data and the materials of highway vertical alignment in Zhejiang Province,this thesis analyzed the influence of the highway vertical alignment index and its combinations on traffic safety from the perspective of human,vehicle,highway and environment,and studied the relationship between traffic safety and highway vertical alignment index including setting frequency of grade change point,longitudinal gradient,grade length,grade difference at grade change point,vertical curve radius,length as well as their combinations including average gradient of continuous downgrade,grade length and the entrance and exit of the tunnel.At the same time,the relation curve between the accident rate and the setting frequency of the grade change point,longitudinal gradient and grade length was established,and then the relationship between the grade length and the accident rate under different longitudinal gradient conditions was analyzed and the relationship curve was fitted,which provide a basis for the safety design of the highway longitudinal section.In addition,the relationship between the highway vertical curve and the traffic safety was also studied,in which the accident distribution characteristics of the vertical curve sections with different radius and lengths were analyzed,and the relation curve between the vertical curve radius,length and the accident rate was fitted to provide the basis for the design of the highway vertical curve.The vertical alignment combination sections mainly studied the relationship between the traffic safety and flat and vertical combination sections,the alignment of the continuous downgrade sections and the entrance and exit sections of the tunnel.This study analyzed the relationship between radius rate of vertical curve and horizontal curve,vertical curve rate of grade change point and horizontal curve,and traffic safety in flat and vertical combination sections.It then analyzed the distribution characteristics of accidents with increasing grade length for continuous downgrade sections under different average gradients,focusing on the analysis of the relationship between vertical gradients and traffic safety at the entrance and exit sections of tunnel.A model for the relationship between alignment of continuous downgrade section,the longitudinal gradients of tunnel at the entrance and exit,and the accident rate was established.Finally,combined the severity of accidents,the principal component analysis method was used to analyze the accident conditions of distribution characteristics of the continuous downgrade section and the entrance and exit section of the tunnel with linear changes.Through the analysis of the relationship between vertical alignment indicators and their combinations and traffic safety,this study provides the basis for the safety design of highway vertical alignment and offers reference to the designers.