Heriberto Perez, a researcher at the UPV/EHU’s Faculty of Engineering-Bilbao, has developed behavior models able to predict the future deterioration of roads. The models focus on two different aspects, the international roughness index (IRI) and the coefficient of transverse friction. The purpose of the models is to predict when roads will require repair, the type of repair work that will be required, and the projected cost of the work.

In the early 1980s, road roughness was identified as a key indicator of the convenience of highways to road users. Unfortunately, any methods being used to measure road roughness was not consistent or reproducible. As a result, the United States National Cooperative Highway Research Program started a research project in order to improve and standardize the process. The World Bank took over the work to determine how the data collected from different countries could be compared. World Bank tested determined that most equipment had the ability to produce usable measures of roughness if the methods were standardized. Out of that came the International Roughness Index, which defined and tested the roughness scale.

The International Roughness Index is used to manage pavements, to evaluate new construction, and to identify specific areas needing repairs or improvement. The IRI also pays a key role in determining the economic feasibility of road improvement projects based on vehicle operating costs.

The IRI is the worldwide standard for measuring road smoothness longitudinally (in the direction of driving). The IRI measures the roughness of the pavement by the number of meters per kilometer that a laser jumps as it driven down a road. The higher the IRI, the rougher the pavement.

The coefficient of transverse friction measures the available skid resistance perpendicular to the direction of travel and allows the vehicle to change direction. Friction requirements are higher at certain areas such as when nearing a junction or intersection, on a horizontal curve, or going down a slope. Skid resistance is a safety concern, especially when the roads are wet, as wet surfaces provide lower levels of friction. Studies show a strong correlation between the risks of an accident due to skidding and the skid resistance of the pavement. Vehicles travelling on pavements with coefficient of friction lower than 0.45 are 20 times more likely to have an accident than vehicles travelling on pavements with a coefficient of friction higher than 0.60. A lower coefficient of transverse friction indicates a greater chance of accidents occurring. Pavement macro texture is the strongest factor affecting pavement skid resistance when traveling at high speeds.

Perez focused on the highways in Bizkaia for the needed data, from which he developed the behavior models. The IRI model developed by Perez is suitable for any conventional two-lane highway made of a flexible or semi-rigid pavement. The transverse friction model is adaptable to any type of road made of any traditional material. Future use of these models will hopefully lead to improved roads, fewer accidents, and reduced costs for highway repairs all around the world. Using the models, it is possible to determine the condition of a road several years in the future after a certain number of vehicles have traveled along the road. From there, planners can strategize to maximize the benefits of any future repairs while minimizing costs. Research continues into why some sections of highways deteriorate more quickly than other sections.

Furhter information: Heriberto Pérez-Acebo et al. Skid resistance prediction for new two-lane roads, Proceedings of the Institution of Civil Engineers – Transport (2017). DOI: 10.1680/jtran.17.00045