## 2 Materials and Methods  
### Decision Process Model  
The proposed pavement service life decision process algorithm, shown in Figure 1, is designed to include the necessary subsystems to maintain the required pavement service life. It is based on calculations of pavement structural condition, derived from residual structural life, and the progression of pavement serviceability, based on preventing unnecessary deterioration. These elements are integrated into the pavement asset value calculation. Since pavement is part of the road and the broader road network, the road asset value should also be included in the process. Finally, the algorithm incorporates economic assessment and optimization of rehabilitation. The outputs are pavement and road rehabilitation programs, constrained by limited financial resources and funding eligibility requirements. While Big Data is shown in the flowchart as a potential input, the presented methodology primarily relies on conventional data sources available in road inventory databases maintained by road authorities. The mention of Big Data reflects anticipated future developments rather than current implementation. As evident from the pavement asset value calculations, it is essential to know the rate of pavement deterioration, which is determined using the structural pavement condition. This condition is expressed by calculating the structural life expectancy and its ratio to the design life. From the perspective of pavement design, the residual service life is a crucial parameter. To calculate the structural life expectancy, the crack initiation criterion is used, in accordance with the design methods for flexible and semi-rigid pavements. This criterion ensures that the radial stress at the bottom edge of the base course remains below its critical material strength. This condition can be expressed as an inequality, shown in Equation (1) [64; 65]:  
\[\sum_{i=1}^{n}Q_{i}\times\frac{\delta_{n,i}}{SN_{i}*R_{i,I}}\leq 1 \tag{1}\]where \(\sigma_{r,I}\) denotes radial stress at the bottom of the base course during period \"\(i\)\" when subjected to the design axle load in MPa; \(R_{i,I}\) is the computed flexural tensile strength value of the base course material being assessed under the conditions in period \"\(i\)\" in MPa, and \(S_{N}\) is the fatigue coefficient. Figure 1: Pavement service life decision process algorithm. When designing a new pavement, Equation (1) is applied as standard, as the material characteristics are defined by standard parameters--namely, the modulus of elasticity and Poisson's ratio. The challenge arises when calculating stresses for older, in-service pavements. In such cases, the back-calculation method must be used, based on falling weight deflectometer (FWD) measurements and a numerical elastic deformation model in a layered elastic half-space. The output of the back-calculation method is the actual elastic moduli of the surfacing course, base course, subgrade, and subsoil. When these values are substituted into Equation (2) [64; 65], the real current radial stress data are obtained. The actual calculation of structural life expectancy is based on fatigue coefficients, denoted as coefficients 'a' and 'b' in the following equation. To derive these coefficients, it is essential to experimentally determine the parameters that define fatigue characteristics, representing the pavement's resilience to repetitive loading. In this test, a sample of the pavement surfacing layer is subjected to repeated bending. The results are presented in a Wohler diagram, as shown in Figures 2 and 3. Radial stress and strength resiliency values in ACM layers based on DAL are shown in Table 1.  
\[log\ \varepsilon_{0j}=a_{j}+b*logN \tag{2}\]  
where \(\varepsilon_{0j}\) is the maximal amplitude of proportional deformation in the initial phase of measurement; \(a\), \(b\) are fatigue parameters that define the stress lines coefficient over a range of \"N\", and \(N\) is the number of load repetitions. Figure 3: Wohler diagram AC16-L base course (bitumen grade 50/70).