## 4 Conclusions  
In this study, four kinds of bituminous mixture modification schemes were selected and tested, and the pavement performance of these polymer-modified bituminous mixtures was evaluated.  
1. Based on the location of the actual engineering, five main influencing factors were analyzed, including high-temperature stability, low-temperature crack resistance, water stability, fatigue resistance and economy. The corresponding performance results were obtained as the scoring basis for the optimal decision making for the bitumen middle course scheme.
2. The fuzzy comprehensive evaluation method was used to conduct the comprehensive analysis, and the combined weight method of the analytic hierarchy process and EW was used to calculate the index weights, reducing the influence of subjective factors to a certain extent.
3. Through a case analysis, according to the final evaluation matrix and the principle of maximum membership degree, the comprehensive ranking of schemes could be obtained, 70\({}^{\text{th}}\)+M \(>\) 70\({}^{\text{th}}\)+PR \(>\) AR \(>\) SBS, and it was evident that the polymer-modified bituminous mixture (70\({}^{\text{th}}\)+M) had the best overall performance.
4. The application of (70\({}^{\text{th}}\)+M) bituminous mixture in engineering demonstrated its robust performance, so the optimization decision method proposed in this paper was feasible. The fuzzy comprehensive evaluation model adopted in this study can also be applied to decision-making analysis for the optimal selection of modified bituminous mixtures in other areas and different sections of bitumen pavement.  
As mentioned in this paper, achieving a balanced performance in the optimization of polymer-modified bituminous mixtures is a great challenge. Currently, a single polymer  
Figure 8: The completed toll plaza in Gongpeng Town, Yushu City.  
Figure 7: Structural composition and material of bitumen pavement in toll plaza.  
cannot give the mixture both high-temperature stability and resistance to low-temperature cracking. Moving forward, our aim will be to innovate a polymer material that ensures not only peak performance for the bituminous mixture but also sustained stability, ease of construction and cost-effectiveness.  
Regarding decision-making methodologies, future studies can consider evaluating the life cycle cost and performance of these mixtures. Factors such as temperature fluctuations, vehicle speed, load, and others, should be weighed in these evaluations. Additionally, adopting comprehensive evaluation methods like the interval-valued picture fuzzy set for selection [51] and multi-source fuzzy comprehensive evaluation [52] could enhance the depth and accuracy of decision-making processes.  
Conceptualization, F.W. and W.W.; methodology, F.W. and X.Q.; formal analysis, F.W.; writing--reviewing and editing, F.W.; investigation, X.Q.; data curation, X.Q. and L.X.; writing--original draft, X.Q. and W.W.; validation, W.W.; visualization, G.Z. and L.X. All authors have read and agreed to the published version of the manuscript.  
This research was supported by the Science and Technology Project of Jilin Provincial Department of Transportation (2017 ZDGC-8). The authors gratefully acknowledge its financial support.  
Not applicable.  
The data presented in this study are available on request from the corresponding author. The data are not publicly available due to commercial reasons.  
The authors especially thank their project partners, the Jilin Provincial Department of Transportation.  
The authors declare that they have no conflicts of interest.