Full-scale accelerated testing was used to provide new insight into quantifying the effectiveness of geogrids on low-volume flexible pavement performance. Although several previous studies report that geogrids improve pavement performance by enhancing structural capacity and reducing distress potential, the new study addresses how to maximize the benefits and cost-effectiveness of geogrid. To perform full-scale testing, three cells of flexible pavements, each having three pavement sections, were constructed. The granular base and hot-mix asphalt (HMA) layer thicknesses varied, and each cell had at least one control and one geogrid-reinforced pavement section. Instruments were embedded during construction to measure stress, strain, deflection, moisture, pore-water pressure, and temperature and were used to monitor pavement response to moving load. A moving dual-tire at 8 km/h and 44 kN was used to apply accelerated traffic loading. The performance of the various pavement sections when exposed to accelerated loading is presented. On the basis of pavement measured response as well as visual observation of the pavement cross section after excavation, the study showed that geogrid is very effective in reducing the horizontal shear deformation of the aggregate layer, especially in the traffic direction. Hence, the effectiveness of geogrid is clear for aggregate base layers with thicknesses ranging from 203 to 457 mm, and geogrid is expected to show similar effectiveness for greater base thickness given that thin HMA layer is used. The study also found that the optimal geogrid location in a thin aggregate layer is at the unbound aggregate-subgrade interface. For a thicker base layer, it is optimal to install a single geogrid at the upper third of the layer; the addition of another geogrid at the subgrade-base layer interface may be needed for stability.