Unlike other pavement indices, the skid resistance, or friction, of bituminous pavements behaves differently. After the extension of a new layer, the friction increases as the bitumen film is removed and the aggregates are exposed. The aggregates are then polished by traffic, mainly by heavy vehicles, and the pavement reaches the seasonal phase, in which, if heavy traffic volume remains constant, the only variations are seasonal, with maximum values in winter and minimum values in summer. Nonetheless, in tunnels, as they are not exposed to climatic actions, the friction value is lower than outside. Therefore, the article evaluates the skid resistance decrease in tunnels compared to outdoor conditions. For this purpose, the skid resistance values in dual-carriageway tunnels in Gipuzkoa (Spain) were studied and compared with the values obtained 500 m before and after the tunnel. Overall, a 10% friction decrease was observed inside the tunnels. In winter, the decrease was 11%, while in summer it was 8%. In tunnels longer than 500 m, the decrease was greater (12%) than in tunnels shorter than 500 m (9% and 7%). This analysis contributes to a better knowledge of the available friction inside a tunnel and to the better management of road safety.

Skid resistance, or friction, on a road surface is a critical parameter in functional highway assessments, given its direct relationships with safety and accident frequency. Therefore, road administrations must collect friction data across their road networks to ensure safe roads for users. In addition, having a predictive model of skid resistance for each road section is essential for an efficient pavement management system (PMS). Traditionally, road authorities disregard rural roads, since they are more focused on freeways and traffic-intense roads. This study develops a model for predicting minimum-available skid resistance, which occurs in summer, measured using the Sideway-force Coefficient Routine Investigation Machine (SCRIM), on bituminous pavements in the single-carriageway road network of the Province of Gipuzkoa, Spain. To this end, traffic volume data available in the PMS of the Provincial Council of Gipuzkoa, such as the annual average daily traffic (AADT) and the AADT of heavy vehicles (AADT.HV), were uniquely used to forecast skid-resistance values collected in summer. Additionally, a methodology for eliminating outliers is proposed. Despite the simplicity of the model, which does not include information about the materials at the surface layer, a coefficient of determination (R²) of 0.439 was achieved. This model can help road authorities identify the roads for which lower skid-resistance values are most likely to occur, allowing them to focus their attention and efforts on these roads, which are key infrastructure in rural areas.

More than 90% of the road network of Loja, Ecuador, is unpaved and lacks an official condition metric. Low-cost measures relate to the IRI on pavements, but not demonstrably on unpaved roads. A 15 km Andean corridor was surveyed in one dry season with four visual–manual indices (URCI, MTC, PASER, ICNP), a Class III profilometer, and an uncalibrated smartphone application, over 150 stations harmonized from 60 native index observations, 30 for the MTC. A single profilometer run was moderately reliable (ICC = 0.631, 95% CI 0.559–0.699); four runs averaged 0.872, so repeated runs are a quantified requirement, not a convention. The application erred in level, not in spatial pattern (standardized ICC = 0.900), placing 88.7% of stations within one quartile of the reference: its role is segment-scale screening, not absolute IRI. Under leave-one-block-out spatial validation, the index–IRI equations retain an R² of 0.32–0.40; MTC was the only index whose association depended on the measuring instrument (p = 0.010). Surveying on foot cost 4.45–12.36 USD/km against 23.68 for reference profilometry, whose largest item is the vehicle. A tiered cost–accuracy architecture is proposed, with URCI and ICNP as preliminary candidates for official adoption, subject to validation based on further corridors and in wet condition.