Study On The Relationship Between Traffic Safety And Vertical Section Parameters Of Continuous Downhill Road

With the effects of terrain,environment and building cost of projects,it is inevitable to set up a few kilometers to tens of kilometers continuous downhill grades on many highways. Although the length and grade of a single slope do not contravene the standards of road designing,actually there is serious hidden danger about safety for continuous downhill grades.Especially on the mountainous highway,simultaneously with the effects of small radius curves and bad visual field,the sections of continuous downhill road often become hazardous sections.Based on the data of eight different levels continuous downhill roads,the relationship between traffic accident and vertical parameters is researched.By the contrast and analysis of the lengthwise distribution profiles of traffic accidents and grades of eight road sections, the accident-prone areas or black-spots are found near the base of the continuous downhill road sections.According to samples divided by the designing slope length,significantly linear correlation between the accident rate and the location slope is obtained by the regression analysis.Samples are divided by 500m fixed-length,and based on significant affection of the continuous downhill grades to braking performance and the accidental release of energy theory,the natural profile of upward N(N=0,1,2,3,4.5)km from the accident location,i.e.N km natural profile,is defined as the grade indicator.By the regression analysis,analysis of variance,three remarkable results have been obtained as follows:(a) The indicator of N(N=1,2,3,4,5) km natural profile is superior to the indicator of location slope;(b) The correlation between the accident rate and 2km or 3km natural profile is most significantly,the goodness of fit is best with the coefficient of determination near to 1;(c) When the 2km or 3km natural profile is greater than 3%～4%, the accident rate increases significantly.In the data analysis,a sample-dealing approach,which is based on "grouping and averaging" concept,is proposed and used.It can balance the affection of other factors and make the correlation between the accident rate and grade indicators more significant.