## 6 Conclusions  
Based on the analysis of the current research status of preventive maintenance timing decision-making at home and abroad, this study starts from the aspects of LCCA and LCA, establishes a comprehensive decision-making method and model for maintenance timing from economic, social, and environmental aspects, and selects maintenance plans with high economic efficiency and small environmental impact throughout the entire life cycle for maintenance projects. It also improve the scientific nature and sustainable development level of road maintenance decision-making. Through case analysis, the following conclusions can be drawn:  
(1) Integrated LCCA and LCA by the principle that energy consumption and air pollutants, e.g., CO\({}_{2}\), HC, NOx, and CO, were assigned monetary values for unit mass. Then the environmental damage cost computed by multiplying unit price with energy \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Time for Taking** & **Comprehensive Benefits** & **Present Cost** & **Benefit Cost Ratio** \\ \hline
4 & 0.47 & 8114.22 & \(5.8\times 10^{-3}\) \\
5 & 0.65 & 8082.65 & \(8.0\times 10^{-3}\) \\
6 & 0.62 & 8109.17 & \(7.6\times 10^{-3}\) \\
7 & 0.44 & 10,668.18 & \(4.0\times 10^{-3}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 28: Benefit Cost Ratio. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Year** & **\(\Delta\)FCC** & **\(\Delta\)WC** & **\(\Delta\)RC** & **\(\Delta\)TTC** & **\(\Delta\)AC** & \(\begin{array}{c}\mathbf{\Delta EEC}_{\text{\bf{oper}}}\end{array}\) & \(\begin{array}{c}\mathbf{\Delta EEC}_{\text{\bf{oper}}}\end{array}\) & \(\begin{array}{c}\mathbf{\Delta EEC}_{\text{\bf{oper}}}\end{array}\) & \(\begin{array}{c}\mathbf{\Delta EEC}_{\text{\bf{oper}}}\end{array}\) & \(\begin{array}{c}\mathbf{\Delta EEC}_{\text{\bf{oper}}}\end{array}\) & \(\begin{array}{c}\mathbf{\Delta EEC}_{\text{\bf{oper}}}\end{array}\) & \(\begin{array}{c}\mathbf{\Delta EEC}_{\text{\bf{oper}}}\end{array}\) & \(\begin{array}{c}\mathbf{\Delta NC}_{\text{\bf{oper}}}\end{array}\) \\ \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} \\
2 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\
3 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\
4 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\
5 & 5.61 & 0.1052 & \(2.03\times 10^{-5}\) & 5.784 & 0.351 & 0.0606 & 0.0030 & 0.1270 & 0.00019 & 8.28 \\
6 & 6.00 & 0.1013 & \(1.98\times 10^{-5}\) & 5.765 & 0.360 & 0.0648 & 0.0033 & 0.1359 & 0.00020 & 8.86 \\
7 & 6.42 & 0.1003 & \(1.921\times 10^{-5}\) & 5.720 & 0.368 & 0.0693 & 0.0035 & 0.1454 & 0.00022 & 9.47 \\
8 & 6.88 & 0.1015 & \(1.87\times 10^{-5}\) & 5.645 & 0.376 & 0.0742 & 0.0037 & 0.1556 & 0.00023 & 10.14 \\
9 & 7.36 & 0.1042 & \(1.82\times 10^{-5}\) & 5.538 & 0.382 & 0.0794 & 0.0040 & 0.1665 & 0.00025 & 10.85 \\
10 & 7.85 & 0.1081 & \(1.77\times 10^{-5}\) & 5.393 & 0.387 & 0.0847 & 0.0043 & 0.1777 & 0.00027 & 11.58 \\ \hline \hline \end{tabular}
\end{table} 
Table 27: Calculation Table for Present Value of Benefits. consumption and air pollutant mass, together with agency cost and user cost, was treated as inputs for the LCCA. (2) In the process of building the cost model, consider the costs caused by the maintenance and construction processes to users and the environment, and provide an improved calculation method to estimate the fuel consumption and environmental emissions associated with speed changes through the work zone areas. (3) A functional relationship between user cost-saving benefits, environmental cost-saving benefits, and pavement performance was constructed. Considering the economic, social, and environmental benefits of each maintenance plan, a comprehensive evaluation model for highway pavement maintenance benefits was constructed using the AHP.