In the highway safety audit，the application of highway alignment parameters has a certain impact on highway traffic safety. In addition, the latest Design Specification for Highway Alignment in China don’t explicitly give specific design requirements or provisions on the quantitative and definite radius ratio of horizontal and vertical curve. Therefore, this paper makes full use of horizontal and vertical alignment index information of six roads and statistics of accidents, in order to explore the relation between horizontal and vertical curve radius ratio and road accident rate. First, carry on the road section, and classify accidents according to concave and convex vertical curves，and the curve radius size respectively. Then study the effect of horizontal and vertical curve radius ratio on the accident rate. The influence of ratio change on the accident rate is found out, but also the sensitivity of the correlation between the two. The accident rate of each section is represented by (per mile and per 10,000 vehicles)^(-1). Finally, the reference value of the recommended range of the ratio of horizontal and vertical curve radius is obtained, according to the analysis conclusion. The results show that the accident rate is lower than that of adjacent sections with other ratios when the radius ratio of horizontal and vertical curves is between 14 and 22. However, when the radius ratio is about 10, and the accident rate has begun to decline. When the radius of the horizontal curve is less than 1000m and the radius ratio is 12-22, the accident rate is relatively low, and maintains a relatively low level with the increase of the ratio (over 26).When the radius of the plane curve is greater than 1000m, and the ratio is greater than 12, the accident rate basically maintains below 10 (per mile and per 10,000 vehicles)^(-1).In addition, it is found that the accident rate is relatively high when the radius ratio of the horizontal and vertical curves is between 6 and 12.

CICTP