Open-graded aggregate base courses have been increasingly used in Portland cement concrete (PCC) pavements as one of the effective strategies for improving subsurface drainage efficiency and thus pavement longevity. In addition to maintaining adequate permeability, these layers are also required to remain stable during pavement construction, performance period and future rehabilitation activities. In an effort to study subsurface drainage and stability of a new open-graded aggregate base material (OGAB Special) under construction, PCC pavement test sections (Cells 306 and 406) were constructed by the Minnesota Department of Transportation (MnDOT) on the 3.5-mile mainline interstate roadway segment at the MnROAD test facility in 2011. Both test cells consist of 6-in. thick PCC slab, 6-in. thick OGAB Special layer and 7-in. Class 5 (MnDOT traditional dense-graded) unbound aggregate underlain by clay subgrade. This paper presents the findings from analyzing field instrumentation data and Falling Weight Deflectometer (FWD) test results to assess the effectiveness of the OGAB Special layer in controlling subsurface moisture regime and providing structural stability. For comparison, field test data were also collected and analyzed from MnROAD Cells 38, 53, and 54 that are located in the low-volume roadway segment and consist of PCC slabs of similar thickness and traditional dense-graded base layers (Class 5 or 6) underlain by clay subgrade. It was concluded from analysis results that the OGAB Special layer cannot only reduce the subsurface moisture content significantly but also provide comparable structural stability, as compared to traditional dense-graded (Class 5/6) base layers.