To prevent the deleterious effects of undrained moisture in pavement structures, it has become common to incorporate subsurface drainage features such as permeable bases and edge drains into pavement design. A theoretical design methodology has been developed to ensure that the level of subsurface drainage is adequate for the specific pavement structure. However, recent research has called into question the effectiveness of subsurface drainage for certain types of pavement structures. Correlating the presence of moisture-related pavement distress with drainage features has revealed that drainage features do not significantly reduce faulting of doweled jointed concrete pavements, and that edge drains may negatively impact hot-mix asphalt pavements. However, the study in which this correlation was accomplished did not attempt to assess the adequacy of the provided drainage features using the theoretical design methodology. This research presents an alternative method of effectiveness assessment based on design adequacy. The theoretical drainage capacity of a design feature, such as a pavement base or edge drain system, is computed using the design methodology and compared with the expected inflow to that feature. The adequacy of the design is expressed as the proportion of the computed capacity to the expected service requirement. The method is applied to cases in the Long-Term Pavement Performance database. Examples are provided in which adherence to the design methodology would have indicated that the drainage features were inadequate; however, the more simplistic observational approach would reflect poorly on the effectiveness of the provided drainage features.