## 1 Introduction  
Processing the service life of the pavement at the required level is crucial, considering that the pavement materials embedded within the pavement structure gradually lose their original properties due to traffic loads and climatic conditions. The resulting loss of structural integrity and pavement serviceability requires a sustainable approach through technically and economically efficient rehabilitation methods. To maximize pavement service life at minimal cost and make informed decisions regarding the use of reinforcing overlays or complete reconstruction using new or recycled materials, a comprehensive decision process is indispensable. This process prioritizes various factors, including the condition of the pavement and its subsystems, such as the structural pavement condition, pavement serviceability, calculation of pavement asset value, economic assessment, and optimization of pavement rehabilitation. Structural pavement condition refers to the pavement's ability to withstand traffic loads and represents its current state relative to its pristine condition. It is represented by the residual structural life as a proportion of the design life. The demand for a precise expression of the structural pavement condition led to the development of a new methodology, which determines the pavement's residual structural life and its ratio to the design life using analytical-experimental measurements and calculations. The method for calculating residual structural life is based on a mathematical model of a layered elastic half-space and fatigue experimental tests. To apply this equation in determining residual structural life, it is necessary to ascertain the actual modulus of elasticity and strength, particularly in the base course of the pavement. These values are estimated during the evaluation of pavement load-bearing capacity using a falling weight deflectometer [1,2]. The falling weight deflectometer imparts an impact on the pavement, eliciting a flexible response in the form of a deflection bowl. The configuration of this bowl reveals the deflection measurements from individual sensors affixed to the pavement at specific distances from the impact point. Through a process referred to as back-calculation [3,4], the actual modulus of elasticity for each pavement layer is computed within a layered elastic half-space model [5, 6, 7]. Subsequently, based on the modulus of elasticity, the stresses in the pavement layers are determined [8, 9, 10, 11]. Following the calculation of the stresses and strains in the pavement structure in its actual condition, it is then possible to calculate the residual life based on experimentally obtained fatigue parameters of asphalt concrete pavement materials, as defined by the European standard [12,13]. Pavement serviceability refers to the pavement's ability to provide a safe, economical, and comfortable ride and traffic quality. Pavement serviceability is expressed in terms of roughness and surfacing damage. Roughness and surfacing damage may not always be related to the bearing capacity of the pavement and can often be repaired with thin overlays. However, roughness is generally linked to the overall pavement structure and its bearing capacity. Therefore, it is necessary to assess pavement condition based on the level of bearing capacity. The evaluation includes longitudinal and transverse unevenness and their impact on vehicle operating costs and travel time costs. To derive reliable mathematical deterioration functions, accurately measured real pavement degradation data must be obtained either through analytical and experimental tests conducted in an advanced accelerated pavement testing facility or by analyzing long-term pavement performance data collected through rigorous diagnostic procedures and stored in a road asset inventory. The progression of these adverse changes can be mathematically expressed through degradation functions known as pavement performance models [14, 15, 16, 17, 18, 19, 20].