Exploratory Baseline Monitoring of International Roughness Index (IRI) Evolution on an Andean Mountain Corridor Under Data-Constrained Conditions: The Loja–Catamayo Highway, Ecuador

Systematic spatiotemporal records of the International Roughness Index (IRI) for South American Andean rural corridors remain scarce, and available deterioration models, calibrated mostly under temperate or arid conditions, transfer to Andean tropical contexts with considerable uncertainty. This exploratory baseline study addresses that gap on the 36.50 km Loja–Catamayo corridor in southern Ecuador under three a priori constraints: eleven IRI campaigns, one meteorological station whose record starts ten months after the first campaign, and a traffic series anchored on a base-year count conducted ten years before the monitoring window. The campaigns, conducted with a Roughometer III between 2023 and 2025, were integrated with daily climate records from the INAMHI Villonaco station, a yearly AADT series cross-validated against a contemporary classified count, and the as-designed pavement structural section. The non-parametric framework combined the Mann–Kendall trend test with a 25-cell Antecedent Moisture Index sensitivity grid, AASHTO 1993 Structural Number computation, Sayers-derived Present Serviceability Index, and linear, exponential, and Gompertz modelling. The results revealed a statistically significant positive monotonic trend robust to post-peak truncation (H1 supported) and no detectable short-term climate–IRI association under any of the twenty-five AMI specifications tested (H2 not supported at the available resolution). The corridor exhibits a structural reserve exceeding projected cumulative ESAL demand by an order of magnitude yet reached the functional intervention threshold at one-third of its design service life. This decoupling between structural adequacy and functional decay locates the dominant deterioration mechanism in the bituminous surface and the drainage regime, supporting surface preservation interventions as the operationally appropriate response.