# Three-Dimensional Stopping Sight Distance Calculation Method under High Slope Restraint
## 5 Instance Verification
### S.S.D. Inspection Based on Design Speed  
Thus, it can be concluded that the S.S.D. at the bend obtained by the above method is 45-60 m, and according to the provisions of \"Design specification for highway alignment\" (JTG D20-2017), the minimum value of S.S.D. of passenger car for secondary highways of 40 km/h is 40 m, so the six turns meet the requirements of the design specification.  
The method is further verified by the traditional horizontal sightline offset method (Figure 9), which is the distance between the driving trajectory and the line of sight curve. Roadside Design Guide (2011, AASHTO) states that in order to provide sufficient S.S.D., the inside of the flat curve must be guaranteed to have enough H.S.O. (horizontal sightline offset). The H.S.O. required for different radius of the circular curve can be calculated by the S.S.D. with the following Equation (15). If the existing horizontal sightline offset of the project is less than the calculated H.S.O. value, the sight distance does not meet the requirements of the viewing.  
\[m=R\bigg{[}1\ -\cos\bigg{(}\frac{28.655}{R}\bigg{)}\bigg{]} \tag{15}\]  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Intersection** & **PI115** & **PI144** & **PI152** & **PI317** & **PI324** & **PI369** \\ \hline Horizontal S.S.D. (m) & 46.2241 & 56.4194 & 53.0288 & 57.3197 & 57.5940 & 58.3036 \\
3D S.S.D. (m) & 46.2246 & 56.4204 & 53.0296 & 57.3483 & 57.5965 & 58.4897 \\ Difference (m) & 0.0005 & 0.0010 & 0.0008 & 0.0286 & 0.0025 & 0.1861 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Calculation results of S.S.D. at each intersection point.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Intersection** & **Pile No. at the Center of the Curve** & **Radius of Circular Curve (m)** & **Length of Transition Curve (m)** & **Slope** & **Vertical Radius (m)** \\ \hline PI115 & K173 + 859 & 60.8 & 50 & 1:0.3 & 2800 \\ PI144 & K178 + 841 & 85.2 & 35 & 1:0.3 & 2800 \\ PI152 & K179 + 933 & 77.5 & 40 & 1:0.3 & 2800 \\ PI317 & K217 + 119 & 97.4 & 40 & 1:0.3 & - \\ PI324 & K219 + 289 & 90.0 & 45 & 1:0.4 & 1800 \\ PI369 & K229 + 543 & 102.9 & 65 & 1:0.3 & - \\ \hline \hline \end{tabular}
\end{table}
Table 1: The calculation parameters of S.S.D. calculation.  
In the formula:  
\(m\) is the required horizontal sightline offset (m);  
\(R\) is the curve radius (m) at the midline of the inner lane;  
\(S\) is the S.S.D. of the passenger car.  
The existing horizontal sightline offset of the road should include the normal distance from the driver's point of view to the slope of the road. For this project, it includes half lane width, hard shoulder width, side and lining size, slope height, and slope rate. The driver's viewpoint is considered to be a position shifted to the left by 0.3 m from the center axis of the car. In summary, the current H.S.O. of the project is as follows:  
\[m_{0}=0.3+\frac{3.5}{2}+0.75+0.6+0.25+1.2\times 0.3=4.01m \tag{16}\]  
Substituting m\({}_{0}\) into Equation (15) and \(R\) can be calculated. The radius of the right-turning curve needs to reach 59.63 m to meet the safety S.S.D. requirement, and the minimum turning radius in the calculation curve is 60.8 m, so the turn meets the S.S.D. requirements, this is also in line with the calculation results of the calculation method of this paper.