The objective of this research was to investigate the structural capacity of aggregate base materials stabilized with triaxial geogrid placed in a full-scale pavement involving control, or unstabilized, sections. Field testing was performed on a roadway in northeastern Utah that was 16 km (10 miles) long and included 10 test sections, seven stabilized sections and three control sections, each having five test locations. The pavement structure was comprised of a hot mix asphalt layer overlying an untreated aggregate base layer of varying thickness, depending on the test section. Except for the control sections, one or two layers of geogrid were incorporated into portions of the pavement structure at different locations. Falling-weight deflectometer testing and dynamic cone penetrometer testing were used to evaluate the structural capacity of the aggregate base layer in each pavement section. For data analysis, the Rohde's method was applied in conjunction with the 1993 American Association of State Highway and Transportation Officials pavement design guide methodology, and the Area under the Pavement Profile (AUPP) method was applied in conjunction with a mechanistic-empirical pavement analysis. Statistical analyses were then performed to enable comparisons of the test sections. Field results indicated that the asphalt layer thickness was consistently 140 mm (5.5 in.) at all 10 test sections, and the base layer thickness varied from 360 mm (14 in.) to 510 mm (20 in.). The results of the statistical analyses indicated that the majority of the 45 possible pairwise comparisons among the test sections were not statistically significant, meaning that variations in the presence and position of triaxial geogrid at those sections did not appear to affect the structural capacity. The remaining comparisons, however, were statistically significant and involved the test sections with the highest structural capacity. While one of these was unexpectedly an unstabilized control section, the others were constructed using one or two layers of geogrid in the base layer. In addition to being statistically significant, the observed differences were also practically important. Increases in the observed base layer coefficient from 0.12 to 0.18 correspond to an increase in the allowable number of equivalent single axle loads (ESALs) from 5.9 million to 19.2 million at the research site, while decreases in the observed AUPP value from 340 mm (13.37 in.) to 213 mm (8.38 in.) correspond to an increase in the allowable number of ESALs from 3.7 million to 17.3 million at the research site. These results indicate that, when geogrid reinforcement is compatible with the given aggregate base material and proper construction practices are followed, statistically significant and practically important increases in pavement design life can be achieved.