Expansive clay subgrades have been the primary source of damage to many roadways in Texas. The Texas Department of Transportation (TxDOT) has been using geosynthetics to stabilize the base course of the roadways prone to damages induced by expansive clay subgrades. However, the efficiency of this practice has not been fully evaluated. This paper presents the results of a comprehensive field evaluation of several roadways founded on Texas expansive clay subgrades. Geosynthetic-stabilized test sections and control (non-stabilized) test sections were constructed along the identified roadways. Long-term performance of the test sections was evaluated using two independent sources of information: 1) data collected through rigorous condition surveys conducted by the research team, and 2) data collected as part of TxDOT annual performance monitoring program (Performance Management Information System (PMIS)). Reasonably good agreement was found between the evaluations conducted using the aforementioned independent sources of information. Findings from these evaluations were used to develop performance quantification under environmental loads resulting from volumetric changes of expansive clay subgrades. Quantification of such performance has not been previously available. The performance quantification presented in this paper not only underscores significant contribution of geosynthetics to improve the roadway performance under environmental loads, but also highlights the benefits of collecting systematic performance data by transportation agencies (for example through PMIS) to provide objective information on pavement conditions for important decision making on maintenance priorities, rehabilitation strategies, and prediction of pavement performance.