<p>Interlayer bonding condition is a critical yet often oversimplified factor in the mechanistic analysis of asphalt pavements. This study presents a comparative analysis of the algorithmic approaches to modeling interface conditions in four widely used linear-elastic programs: BISAR, KENLAYER, EVERSTRESS, and GAMES. We hypothesize that significant discrepancies in critical pavement responses arise primarily from fundamental differences in how each program's algorithm implements bonding and slip conditions, rather than from material properties alone. A typical four-layer flexible pavement structure was modeled, with the bottom two interfaces assumed to be fully bonded. The analysis focused on the first interface between the surface and base layers, evaluating two extreme states: full bond and full slip. The computed responses-surface deflection, tensile strain at the bottom of the asphalt layer, and vertical compressive strain at the subgrade-were compared. Under full bonding, KENLAYER produced the highest values for all three responses (e.g., deflection = 5.522E-4 m), while EVERSTRESS yielded the lowest. Conversely, under a full-slip condition at the first interface, EVERSTRESS computed the highest values (e.g., deflection = 9.094E-4 m), while GAMES produced the lowest. Notably, KENLAYER and BISAR generated nearly identical results under slip conditions. The divergence in results underscores that the choice of analytical software is not neutral; it is a fundamental methodological decision that directly influences structural evaluation and performance predictions. This work emphasizes the need to conduct immediate validation against experimental field data to calibrate these numerical tools and provides a crucial framework for researchers and practitioners to critically select software based on its underlying algorithms and their applicability to specific pavement interface conditions.</p>