# Influence of the Surface Texture Parameters of Asphalt
## 4 Conclusions  
In this study, the macroscopic texture index and the retroreflection coefficient of indoor rutted specimens and field asphalt pavement were measured, and the correlation between them was determined. Then, single and multifactor models of the influence of the macroscopic texture index on the optical reflection characteristics of asphalt pavement were constructed. The main conclusions are as follows:  
* The abrasion effect of the rutting test had a great influence on the texture index and optical reflection characteristics of asphalt mixtures. After rolling, the S\({}_{1}\), S\({}_{2}\), D\({}_{1}\), D\({}_{2}\), \(\Delta\)q, and R\({}_{\text{ku}}\) of asphalt-mixture specimens with different gradations decreased, while R\({}_{\text{sk}}\) and R\({}_{\text{L}}\) increased. R\({}_{\text{ku}}\) decreased the most, 43.65% for SMA, 16.8% for AC, and 25.15% for OGFC. This phenomenon was mainly related to the morphology change of the asphalt mixture;
* The influence of gradation design on the texture index and the optical reflection characteristics of the asphalt mixture were analyzed. The S\({}_{1}\), S\({}_{2}\), D\({}_{1}\), D\({}_{2}\), and \(\Delta\)q of AC and SMA-graded asphalt mixtures were smaller than those of OGFC, and the R\({}_{\text{L}}\) of AC and SMA was much larger than that of OGFC. The main reason was the difference between coarse aggregate contact behavior and the volume index;
* The model of the influence of a single texture index on the reverse reflection coefficient R\({}_{\text{L}}\) before and after the rutting test could be quantitatively characterized by the quadratic function, and the fitting coefficients were all above 0.95. The model laid the foundation for the study of field pavement;
* In terms of the influence of the multitexture index of asphalt pavement on the inverse reflection coefficient R\({}_{\text{L}}\), the nonlinear model was more accurate than the linear model. The correlation coefficient was 0.92 for the nonlinear model and 0.84 for the linear model. It provided a theoretical basis for the safety design of asphalt pavement.  
In summary, there is a good correlation between the macro- and microtexture parameters of asphalt pavement and the retroreflection coefficient, which can effectively reveal the reflection properties of the pavement material. Since the retroreflection coefficient is not widely used in lighting-design software, further research work will further focus on the relationship between macro- and microtexture parameters and the reduced-brightness coefficient table (r-table). Subsequently, based on obtaining the macro- and microtexture parameters of road surfaces, road-lighting designers can accurately calculate the reflection characteristics at different road positions and optimize the illumination design parameters, such as luminaire installation height, interval, and light-distribution curve.  
Conceptualization, P.X.; methodology, G.Q.; validation, C.Z. ([PERSON]); formal analysis, X.W.; investigation, C.Z. ([PERSON]); resources, P.X.; data curation, X.W.; writing--original draft preparation, P.X.; writing--review and editing, H.Z.; visualization, C.Z. ([PERSON]); supervision, G.Q.; project administration, H.Y.; funding acquisition, P.X. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Key Research and Development Program of China, grant number 2022 YFB2601900; the National Natural Science Foundation of China, grant number 52227815; and the Open Fund of Hunan Key Laboratory of Smart Roadway and Cooperative Vehicle-Infrastructure Systems (Changsha University of Science and Technology), grant number kfj210701.  
Not applicable.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Weight** & \(R_{\text{L}}\) \\ \hline Node1 & 0.856 \\ Node2 & 1.893 \\ Node3 & 0.095 \\ Node4 & \(-\)0.977 \\ \hline \hline \end{tabular}
\end{table}
Table 8: Weight relationship between hidden and output layers.