## 3 Construction of Performance Assessment Indicator System for Existing Asphaler  
### Pavement in Highway Renovation and Expansion Project  
The current assessment of asphalt pavement performance in China primarily relies on the PQI evaluation model, with the calculation formula of this model shown in Equation (1). \[\text{PQI}=w_{\text{PCI}}\text{PCI}+w_{\text{RQI}}\text{RQI}+w_{\text{RDI}} \text{RDI}+w_{\text{PBI}}\text{PBI}+w_{\text{PWI}}\text{PWI}+w_{\text{SRI}} \text{SRI}+w_{\text{PSSI}}\text{PSSI} \tag{1}\]  
where PQI, PCI, RQI, RDI, PBI, PWI, SRI, and PSSI, respectively, represent the pavement maintenance quality index, pavement surface condition index, riding quality index, pavement rut depth, pavement bumpiness index, pavement wear index, pavement surface skid resistance index, and pavement structural strength index; \(w_{\text{PCI}}\), \(w_{\text{RQI}}\), \(w_{\text{RDI}}\), \(w_{\text{SRI}}\), \(w_{\text{PBI}}\), \(w_{\text{PWL}}\), and \(w_{\text{PSSI}}\), respectively, represent the weights of PCI, RQI, RDI, PQI, SRI, PBI, PWI, and PSSI in the PQI model; and \(w_{\text{PSSI}}\) takes a value of 0. According to Equation (1), the PQI model incorporates elements such as surface condition, riding quality, skid resistance, rutting, etc. However, further discussion is needed on the following aspects to evaluate the performance of existing asphalt pavement in highway renovation and expansion projects:  
1. [label=(0)]
2. PSSI is not factored into the PQI calculation, rendering the model unable to reflect the pavement's structural condition. 2. Indicators such as PBI, PWI, and SRI, which are associated with pavement safety, are seldom considered in the pavement design of highway renovation and expansion projects, leading to redundant indicators. 3. The weights assigned to these indicators are fixed, resulting in a lower PQI evaluation when a particular indicator deteriorates, which may not effectively guide decision-making in the design of the asphalt pavement for highway renovation and expansion projects. The primary objective of assessing asphalt pavement performance in highway renovation and expansion projects is to gauge the condition of existing asphalt pavement. Thus, when establishing a performance assessment indicator system for existing asphalt pavement in highway renovation and expansion projects, it is crucial to highlight common issues and accurately reflect the pavement's load-bearing capacity. Based on the aforementioned considerations, it is evident that there is a need to develop a new performance assessment indicator system for existing asphalt pavement in highway renovation and expansion projects. Drawing from existing literature [26; 27; 28], five asphalt pavement performance evaluation indicators were selected, including RQI, R\({}_{\text{r}}\), C\({}_{\text{r}}\), P\({}_{\text{r}}\), and PSSI, to construct a comprehensive performance assessment indicator system for existing asphalt pavement in highway renovation and expansion projects. These five indicators provide a holistic view of pavement performance across various dimensions, as illustrated in Figure 1.  
The calculation methods for RQI and PSSI are based on the Chinese standard (JTG 5210-2018) [3]. The calculation methods for R\({}_{\text{r}}\), C\({}_{\text{r}}\), and P\({}_{\text{r}}\) are presented in Equations (2)-(4), respectively. \[R_{\text{r}}=\frac{\text{A}_{\text{R}}}{\text{A}}\times 100\% \tag{2}\]  
\[\text{C}_{\text{r}}=\frac{\text{A}_{\text{C}}}{\text{A}}\times 100\% \tag{3}\]  
\[\text{P}_{\text{r}}=\frac{\text{A}_{\text{P}}}{\text{A}}\times 100\% \tag{4}\]  
where A\({}_{\text{R}}\) represents the pavement surface area with a rutting depth greater than 7 mm, calculated by multiplying the rutting length (m) by 0.4 m; A\({}_{\text{C}}\) denotes the crack area, encompassing alligator cracking, block cracking, transverse cracks, and longitudinal cracks, and the area is determined according to the standard JTG 5210-2018 [3]; A\({}_{\text{P}}\) signifies the patching area; and A represents the survey area.