# MILP-Based Approach for High-Altitude Region Pavement Maintenance Decision Optimization
## 2 Problem Formulation  
For roads, high-altitude regions experience harsher climates compared with lower-altitude regions, including factors such as temperature, rain, snow, and ultraviolet radiation. Pavement diseases impact driving safety and user experience, necessitating targeted maintenance. Maintenance decision-making based on inspection data is one method where the pavement condition index (PCI) is a widely used indicator [2; 3; 10; 12; 16]. As shown in Table 2, a Chinese standard named \"Technical Code of Maintenance for Urban Road (CJ) 36-2016)\" [26] classifies pavement distress levels based on the PCI range. Implementing appropriate pavement maintenance can effectively overcome pavement distress, thereby enhancing the pavement condition [8]. As shown in Figure 1, at time \(t_{0}\), the PCI value of a certain road segment is at an ideal level. If no maintenance is carried out, this index will drop to the minimum requirement at time \(t_{01}\). If maintenance is performed at time \(t_{1}\) (\(t_{1}\) is greater than \(t_{0}\) and less than \(t_{01}\)), the maintenance can improve the PCI \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Road Type** & **Excellent** & **Good** & **Qualified** & **Unqualified** \\ \hline Expressway & [90; 100] & [75; 90] & [65; 75] & [0; 65] \\ Main/secondary roads & [85; 100] & [70; 85] & [60; 70] & [0; 60] \\ Branch roads & [80; 100] & [65; 80] & [60; 65] & [0; 60] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: PCI value range-based classification of pavement distress. value at time \(t_{1}\) with a certain level of effectiveness and extend the acceptable PCI value from \(t_{01}\) to \(t_{11}\). When implementing pavement maintenance, it is necessary to consider the corresponding constraints, especially when there are many segments to be maintained. Common constraints include maintenance approaches, budget, and pavement condition indicators [3,8,13]. For high-altitude areas, there are typical characteristics, which include the following:  
1. Seasonality characteristics of maintenance work: The duration of cold seasons with low temperatures is long, and some pavements may even be covered with snow for extended periods. To ensure maintenance quality, pavement maintenance should preferably not be conducted in such seasons or months. 2. Seasonality characteristics of traffic flow: Traffic flow on roads in high-altitude areas is fluctuant. For example, in Lhasa city, Tibet, tourism traffic significantly contributes to overall traffic, with many tourists visiting the city during warmer seasons, especially for self-driving tours. Considering the impact of pavement maintenance on traffic, maintenance should be minimized during high-traffic flow periods. 3. Fragility characteristics of the ecological environment: High-altitude regions have less vegetation and a more fragile ecological environment compared with lower-altitude areas. Substantial evidence shows that the carbon emission factor is more significant in high-altitude areas compared with other regions [26, 27, 28, 29]. Therefore, the environmental impact of maintenance work needs to be considered. 4. High-cost characteristics of maintenance work: Due to climate, environment, industrial development, and resource conditions, high-altitude areas are more reliant on maintenance equipment and materials produced in other regions, leading to higher maintenance costs. Manpower costs exhibit similar characteristics. The problem of interest in this paper is how to formulate a feasible maintenance plan while considering factors or constraints such as cost, budget, seasonal impact, fluc  
Figure 1: Effectiveness enhancement due to pavement maintenance. tuation of traffic flow, environmental impact, maintenance approaches, and pavement condition requirements.