Premature deterioration of highway pavements is often attributed to the base and subgrade. In highway construction projects, construction quality control during the subgrade preparation involves nuclear moisture-density testing at specified depths at equally spaced stations along the entire project length. However, the authors' field study at the Ohio-SHRP Test Road revealed that this conventional approach was not effective for minimizing the variability of the subgrade stiffness. First of all, it was not possible to achieve a uniform moisture-density (or dry density) condition throughout the entire project. Secondly, even when the nuclear test data indicated that a fairly uniform relative compaction was established within an area, the subgrade stiffness could still vary significantly. The reasons for this were that the conventional approach could provide only very localized data on the state of the soil compaction and that the relative compaction alone could not be a reliable indicator to describe the soil stiffness. An alternative approach is to employ a rapid, nondestructive stiffness test method, such as Falling Weight Deflectometer (FWD), Dynaflect, and soil stiffness gage (SSG), in the field to monitor the stiffness of the entire thickness directly during the subgrade preparation.